Define “poorly” Regardless, it’s a waste of money to cancel scores. AP scores are self-reported on the application. The ooficial score report only goes to the college you are attending, and the clerical will not care what your scores are.
No. Not unless you need a Subject Test,
Moot. You don’t have to report any scores if you don’t want. Whether you should report is another question. But, in general, for top schools, there is not “making up” weak portions of an application; they want it all to be strong.