Unbalanced

I'm not going to give a full review of this spell, however some points immediately jump out:

1. There are only 2 level 2 spells hitting for 3d8. Both of them are AoE, but they both require enemies to make a save.
2. Both of the spells require an action to cast.
3. Both of them have V, S, M requirements.
4. Neither let you 'precharge' the spell by holding concentration.
5. Neither of them let you choose the damage type.
6. Neither let you keep trying until the enemy fail their save.

This leads to the following conclusion:

• Damage is too high. Any time you start with the strongest spell of a level, and then improve it, that's a cause for concern.
• This spell is damage that essentially skips the action economy for melee fighters.
• It can be pre-cast, and still allow you to use your bonus action the turn you charge in.
• The charge only activates on a hit, allowing you to keep retrying for free until it hits. If you miss with any other spell, it's gone!
• As with all homebrew, there is inherent imbalance because you are adding utility for some classes but not others.

Usually, hybrid characters have to pick casting or attacking. This spell makes the choice a no brainer. The action economy problems need to be addressed. This spell lets you pre-cast, then enter combat and make a full attack action and bonus action without any drawbacks. What's more, you can cast it every round in combat and still make a full attack.

Even without elemental burst, this would be a powerful spell. I think you need to focus on what you are trying to do with this spell. It's two spells combined together and then amped up, it's a little confusing for me.

Advice

Respect the action economy. Make this spell a melee spell attack. If you want to hit multiple, make it an AoE spell, or reduce damage die. Taking Aganazzar’s Scorcher and adding the chromatic effect, reducing the die and changing to a spell attack might be a good place to start.