Totally agree with the others. First navex can seem really tough.
I think you are probably right about changing to the PA28 for Nav.
I did all my training in the C150 and it's a fine little plane for getting about in, but cabin space ??
The Warrior has a nice little pocket for putting your pens in and it'll take a small kneeboard and checklist as well. You can chuck stuff on the back seat too if you need to.
My first Navex was absolutely dreadful (Cranfield, Sywell, Conninton, Cranfield how easy is that ??) The second was not a lot better etc. and yet I got through the QXC without getting lost, lousy landings yes, but I didn't get lost.
Keep plugging on and it should all come together.