Your game is good both visually and in terms of gameplay. The general mechanics of power up (More life you have > more power you get > Bigger you are and thus susceptible to take damage) is a nice loop.
BUT damn this game is a bit too hard for me. Sure it keeps me engage to try and replay multiple times but I think several times it was unfair.
1. I think there is a lack of hearts in game (No heart after each boss, come on, we just had an hard battle). Plus sometimes hearts are just next to projecticle of enemies, it's unfortunate but it happened several times during my playthrough.
2. Sometimes it seems you just can't dodge the bullets of enemies. Your frog even with one heart isn't just fast enough.
Combined with the lack of heart (and the random behind it), I think this are somes points you should consider to improve.
Except from that your game is really good, Congrats, it could totally be a paying one :D