Thanks for playing, and glad you're enjoying it so far! :D
Yeah, from your comment I think you're at the part where you have to route up through D8 into C8 (as you've alluded to). The easiest way to do it is to not bother trying to bounce up the shaft by wall jumping, and instead wall climb + wall jump as appropriate. The timing is a little tricky but should be possible (I might actually go back and tweak that section slightly to make it less finicky post-jam). I've just had a go at it now and the method I used was:
1, Jump and grab the left wall
2, When safe, jump and grab the right wall and climb up in preparation to jump back to the left wall
3. When safe, jump and grab the right wall and climb up and out
And yeah, shells are just collectable so you don't have to worry about them factoring into unlocking rooms/beating the game.
I'd be interested to know how you get on, if you find that section is just too finicky that's a sign that we probably need to polish it up a bit :)