I gave it another go and now it worked without massive issues! :)
Really fun once you got into the game, but also very easy in the end, but this with more polishing, new levels, harder different enemies, would for sure make it fun!
One bug I found, if you're in the upgrade menu, and you go "out" of it with 1, to get back to shooting, the shooting is not working. You can get it back to working if you press upgrade menu and out of the upgrade menu with the E again.
Also wasn't sure if the upgrades were for player & towers or if they had separate ones, that could have been a good add on as well, but obviously for future, since I get that not everything is doable in this short of a time. But I liked the mechanic!