I would like to give you a slightly different answer (at least from the others you received). They are not wrong, but in my opinion the whole thing can be seen from another point of view.
They did however love it and want to continue next week.
Someone said that this is the answer to your question… but I have to disagree. Being a GM is something completely different from entertaining people in a tourist resort. The fun that is built around a table is not up to a GM, but the whole group. Believe me, you will also have fun playing Snakes and Ladders with your closest friends.
You're a GM and this means you're a player like everyone else. I already said that isn't up to you to entertain the others, but it's plain that your role is different. So… how to know if you did well? Change the point of view.
Did you have fun? Probably you did. Were you satisfied by the game?
I can't ever see them completing the mission at this rate :(
From that sad smile, it seems you were not. It seems you ended up a bit frustrated – so frustrated you decided to ask on this site if you did a good job and how you can improve your gamemastering. Ask yourself if you are OK with the idea of doing another ten session like that, or if you think that two more will be enough for you to screw up everything and kill some of your players.
So, I don't want to be rude, but you would like to say that you didn't do a good job.
On the other hand, that's normal. It was your first time. Every one of us had their first time as GM – none of us did a good job. Why? Because the books and forums teach us that a GM has a great responsibility and that it's up to them to entertain the players.
So, our first time (and that's probably what happened to you, and, believe me, to everyone), we want to have everything under control. We know where clues are to be found, we know where bad people are hiding, we know how many children the smith has, we know how many flowers there are in city hall garden, we even know which tavern has the most bitter beer.
And then? Then players ignore everything. They do something completely different from everything we have prepared and they take three hours to do what could be done in twenty minutes. We took three weeks to prepare a perfect world for them and they ignore it. That's frustrating. Where did we go wrong?
Where we went wrong was in wanting or thinking we had to be the ruler. We are not expecting or prepared to be surprised by them. We think that we have to surprise them with our best while it's a bad thing if we are surprised: otherwise it means we didn't prepare well. Wrong! Wrong! Wrong!
Approach you gamemastering as if you're going to watch a movie. You've already watched the trailer: you know what the movie is about, you know who the characters are, you can imagine fairly well how it ends (come on, everybody knew that Frodo would throw that damned ring into Mount Doom even before the beginning of the first movie, and this is true even of people who didn't read the books). What are you missing? What will happen in the middle. You know the beginning, you know the end, but do not try to imagine how they will get to the end. This is entirely up to them. Just write down some checkpoints, but be prepared: it's likely they will bypass them.
Be ready to be surprised. Be ready to endorse all they propose to you. Let them build the world. Let them gamemaster you. You're like a writer with just a start of an idea, who creates the characters but then sees them start to live and to decide how things will happen. This is the greatest thing about being a gamemaster: you let the players thinking you're ruling them, while they are writing an incredible story for you.
Once the story is finished, you'll read it with a certain satisfaction and you'll know you did a great job as a gamemaster.
Paraphrasing Le Moulin Rouge (with a small liberty taken):
The greatest thing you'll ever learn is just to master, and be mastered in return.
PS: Just a side note: only one-and-a-half hours to build PCs?? Great. I admire your group.