Did I scratch off a melanoma
Melanomas and other cancers really can't be just picked off. They leave residual tumor behind. If it was that easy to just pick them off, we wouldn't have to do surgical excisions and such. If you want someone to do a biopsy and confirm what it is, that is fine. (If you are this worried about the site in general this might be a good idea.)
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Scratched off mole
Since you're still very worried I would just go to your dermatologist and get the area punch biopsied. If it was a real melanoma it'd be very difficult to scratch off the entire tumor. There would be some residual tumor left behind. More than likely it was a benign keratosis.