wrote:

Even after about 150 hrs, I do not have the nerve to do spins on my
own because I do not understand them well enough. I am comfortable
with stalls and unusual attitude recoveries of the kind that are
tested on the PPL test but have never done spins with an instructor.

If you are "comfortable" with stalls and unusual attitudes and don't
understand spins, I would suggest that you get some spin training or at
least a better understanding of spins immediately.
Feeling "comfortable" with unusual attitudes without a corresponding
knowledge of spins can be an extremely dangerous combination.
I would suggest strongly that you immediately begin feeling less
"comfortable" with unusual attitudes, or get some basic spin recovery
training as soon as possible. These two items are inseparable.

--
Dudley Henriques