I’m level 8 and my party is level 10.
That’s your problem right there. Druid is a great class, and its spells are its best feature. Natural Spell is also the best druid feat in the game. The wall of ash you get is a great ability—maybe not the best you could possibly ever have, but still pretty great. There isn’t really anything wrong with your choices. You're just two levels behind in a game where every level can double (or more) a character’s power.
This is nearly insurmountable. With all my experience, I could probably build an 8th-level druid that contributes well with your 10th-level fighter or something, but it sounds like your teammates know pretty well what their characters are doing, and in any event at least some of that experience cannot be transferred via a Stack answer.
You should try, if you can, to talk your GM into eliminating the level disparity. Pathfinder has terrible support for split-level parties; I cannot more strongly recommend never having them. Two levels is just, well, like I said, an insurmountable difference. Every player character in Pathfinder should always have exactly the same XP.
That said, we can talk about how to improve the character in general. To begin with, Treantmonk’s Druid Guide—Wild Mystic is great reading. Treantmonk is one of the most experienced writers for both Pathfinder and the D&D 3.5e that it was based on. You’ll notice his Strength is even worse than yours—7!—but he’s got the same 17 Wisdom you do. So you’re not looking too bad there. (His Chapter 2, “Spirit of the Beast,” covers a more melee-centric druid build, but he emphasizes that this is a separate character, not something any one druid can do as well as spellcasting. The third and final chapter, Druid Spells Examined, also has obvious value to you.)
Looking deeper in his guide, we also see Augment Summoning and Natural Spell—two feats you have, also! So again, doing pretty well here. He does recommend delaying Quicken Spell to later levels—which I agree with—but he does call it “an eventual must-have”—which I also agree with. So a small mistake there, but no great blunder. I do disagree with a number of his selections on other feats, though—please don’t take Heavy Armor Proficiency or Improved Natural Armor (on any character, ever) or Toughness (or at least save it for a d6 class that you absolutely cannot get decent Constitution on for some reason). But towards the bottom of the list he does mention Flyby Attack and Hover—the latter I could take or leave, particularly at your level when you can get superior maneuverability that doesn’t need it, but Flyby Attack is amazing so that’s definitely good advice.
And then he goes on to recommend giving up the animal companion. He doesn’t consider subdomains—this guide was written before they existed—but I can assure you that Ash is a distinct improvement over Fire. Fire he rates as kind of a mediocre choice, but with wall of ash I see it as at least as good as Air, Earth, and Water, which he rates more highly than Fire. Overall, the domain options for a druid are limited but they’re still decent.
So, what have we learned from this? Well, first and foremost, that your choices so far really have not been that bad—a lot of them are actually quite close to optimal. That reinforces the notion that the level difference is the real problem. But second, that no one druid should try to do everything druids in general can do. You have lower Strength, higher Wisdom—you are specializing in spells. That’s good, but you have to accept it. With your Strength, you aren’t going to be a melee powerhouse—that's ok! Try using wild shape for mobility and positioning. Flying is great, use it. A hawk raining down fire and ash is quite impressive, and a really good tactic. Again, Flyby Attack helps immensely with that—it’s like Quick Attack, except you can do any standard action in the middle of your movement. Any standard action. Like, you know, casting a spell. Casting spells is how you should be using most of your actions.
For those spells, you want to focus on battlefield control—a druid specialty, and something that any party can appreciate. The wall of ash is great. Summons are pretty good for it too, though the 1-round casting time can be prohibitive. But focus on denying areas to enemies, whatever spells you use to do it—the druid list has many.
Divide and conquer should be your mantra.
Entangle is fantastic, and obscuring mist is not bad either.
Soften earth and stone isn’t just battlefield control, but potentially also utility and exploration.
Sleet storm is just devastating (sadly, it’s pretty much strictly superior than the thematic ash storm at the same level—ash storm is still good, but sleet storm is just better.). Spike growth is another great one. But seriously, you could shove sleet storm into your every 3rd-level-or-higher spell slot and not suck. That spell is absurd.
Spike stones may be pretty basic improvements on spike growth, but it is an improvement, over an already-awesome spell. Ice storm is pretty good, though honestly sleet storm is probably better—eliminating visibility altogether is amazing. Obsidian flow sadly allows a save against its worst effect, but if anyone in your party is tripping people, you just made an area where it is hard to move and getting knocked prone deals extra damage. (Again, the most thematic spell of the level, volcanic storm, is kind of underwhelming.)
Generally speaking, spells that involve clouds, fog, mist, or storms are good. They inhibit visibility, and often also limit mobility. Whether or not they actually hurt someone is, at that point, just gravy.
Also, don’t forget about outside of combat. You have a ton of options here, from using animals as scouts and spies, divining for information yourself, providing great exploration abilities with things like flight or burrowing, and so on. And you have some healing—not worth preparing a spell for most days, but you can keep a wand of cure light wounds handy for topping off between fights, and if something seriously goes wrong, a tactical retreat for a night so you can prepare restoration or reincarnate can be a game-changer.