This is really cool! An RTS is definitely a bold choice for a game jam given the time constraints, but I think you managed to pull off enough to make this a solid little experience. I really like the idea of specifying the different parts of the unit you want to build rather than just picking from a list of units. I could see a really cool system coming out of that where you focus on different attributes for your workers/attackers/etc based on the level and enemies.
I see someone else already pointed out the AudioStream2D issue. On the subject of audio though, I wish there were a bit more sfx going on throughout the game. It feels kind of empty, and then there's suddenly a bunch of gunshots. The first time I attacked an enemy it jump scared me lol.
Overally, great job!