Heeey! As this is the first game you made in Godot it's pretty good. If I understood correctly enemies re-spawn after a certain amount of time (making you "short on time") to force the player to act quickly. This is a promising mechanic that could be improved by indicating the time left before a re-spawn wave, and putting some stress on the player with sound and visual effects. And one other thing that would hugely improve your game: Atmosphere. Any kind of decoration, ambient sound and music could really improve the overall feel of the game.