General advice on how to build more features in less time would be good.
Doing things in 3D is very complex for me, and it seems like it breaks at every step from building to exporting.
I feel you kinda answered your own question - just don't do 3D at start if possible (especially at jams) :) Afaik godot is supporting 2D, just start there. Also if you are new to this, just watch tutorials and try to implement it first without video and if you have problem - then with. I don't think i can give you better answer than this - for doing it more in less time imho you need experience, just try things and you will make it, you are already on right track (practicing instead of only theorizing, you have a good improvement at this week already), good luck! :)
Upd. I was thinking about it a bit more. Also a good thing to do at start is to lower your expectations and scope (especially at jams). For tutorials is better to have some lengthy ones (not for only one element) going from zero to release (at least from zero) so you will learn whole process. In parallel it's mb good to do your own projects tho, to practice solving problems on your own, but mb not focusing on it that much before you release couple of games from other tutorials