This is great for your first game! Everything seemed to work as intended, and I didn't run into any bugs. A couple recommendations:
The bar showing your next jump is a little too far away from the character, so I found myself missing a couple of the longer jumps because I had difficulty looking at both at the same time, making running jumps tricky without running off the edge and dying.
I wasn't able to get past the beginning of the 3rd level, since there's so little time to stay on the platforms without getting attacked. Since the jump time interval seems to be random, there's no telling once you actually jump onto the platforms if your next jump will come in time to get off it. Maybe tweak that part a bit.
Unfortunately, since I couldn't get past that part, I never experienced the boss fight, so I can't say anything about it haha.
But yeah, great stuff for a first attempt! =)