Pretty dank that you made it with something as low-level as SDL2. A pretty cool idea, while nothing revolutionary, was quite fun to play.
I feel like the balance could perhaps do some work (understandable since, speaking from experience, balancing TD games is annoying AF especially when you only have a week for the full game) because initially enemies got absolutely decimated, while at about wave 50ish the enemies became T-34's and started going full Soviet assault on you, but perhaps that was just me sucking at games ¯\_(ツ)_/¯. I also encountered some annoying bugs like if you selected an item while already holding one, the already held item would just get sent to the abyss and be gone forever.
In conclusion, pretty cool and fun, but not without its problems. Overall, great job. (While you're at it, why don't ya check out our TD game :P)