Yeah, as you've mentioned, I can't beat the game now. It really reminds me of that underwater TMNT level on NES.
The character's hitbox felt too harsh, with the game punishing me for being very precise and clearly fitting between the spikes. That should be easy to fix, though, and maybe you could use the health bar to give a little chance to back off when you get spiked.
Well done finishing this little game! ¦3