I looked at the PA voting site and was surprised that there is no advice about what to do if you spoil your ballot.
In CA, the ballot is more like thin cardboard than paper. It has questions on both sides. The instructions say to use ball-point (not gel) black pen.
An instruction sheet is included, and both there and on the mail-in envelope it says what to do if you spoil (mis-mark) your ballot. In some counties you sign a different line on the envelope, enclose the ballot, and send it in for replacement. Other envelopes just say to call, and I've never had to do that.
I realize that your election is Tuesday and it's probably too late for that, so call your county election office and ask what to do!
@bbodb1, your suggestion (as I understand it) would compromise the secrecy of your ballot. When the clerk receives the sealed envelope, she verifies the name, address, and signature against your registration record; if it matches, the envelope is opened and the ballot removed (I think by machine in most places now). At that point the source of the ballot can no longer be identified.