The important thing here is to finish in the deadline of the Ludum. You did your first entry and at least, you have a game, that is what it matters!
I feel pretty unfair that enemies spawn because I dont have time to avoid them (I dont really know where they are! xD). Perhaps you should try to trick the players spawning the enemies far for him (or in a safe radius)
It's important to have time to "polish" the game, for example, you could use another font for the in-game text, or the spawning enemies system.
Anyway, you made a game in 72 hours alone, that is an amazing job so... good job!
Hope we will see in next ludum dares!