First thing's first, the mouse controls give you FAR more control than the keyboard controls will... additionally, unless you're using energy form, you have to aim forward anyway. Now I'll admit to bias here, this was my favorite part of the game and constantly reminded me of Touhou from the epic music to the flood of bullets.
There's no need to cheat through it, its really just a matter of getting used to the area and knowing when to charge and went to use Naija's attack. Generally, you want to save Naija's attack for areas when its really dangerous or for those wall things. It's easier (and safer) to charge Li in some situations than others. Using R to spin, you can shift between the two really easily. Lastly, it sounds like you avoided the more difficult encounters and if that includes the Jelly King, then it'll bite you in the rear. If you had defeated him, you should have earned a jellyfish costume. If you have it, then whenever you run into trouble, you press X to revert to your normal form and simply evade until you auto heal back up to 50%.
This isn't actually that far removed from some of the stuff you had to do for the bosses and enemy encounters, so you should have enough experience to survive it. If you expected this game to be a more mellow run with simple difficulty, I would think that illusion should have been broken in the Cathedral. (for me, it was the nightmare scene) I know this sounds crazy, but its generally normal for games to get really difficult near the end. The games I admire most are those that force me to really pour some effort into some of its encounters, especially the endgame.
Also, if you had trouble with that, there are a few attacks in the final boss that you're gonna hate... most of which are in his first two forms.