Can I fix a bad tube patch?
My last 26" tube cost $8 NZ, so not a lot.  Depends how much time you want to invest, and how much patches cost.

Poor abrading/sanding/scouring ot the area before applying the rubber cement will leave an area of bad adhesion, and the pressurised air can find its way out.   I bet you were in a hurry and didn't give the cement 10 minutes to cure before fitting the patch?  

Bad patches can be a waste of time too - if they're particularly poor quality or excessively cheap, or old or battered then there's a fair chance you'll get poor adhesion.  To be blunt, 48 patches for a dollar from Ebay or alibaba is not generally going to be a good patch.  Old, watery or stale cement/glue can be an issue too.

If your leak is because the patch straddles a ridge then you might be able to shove some rubber cement down there, and then spend a couple minutes pressuring the patch on.  

Problem is that a good patch becomes chemically welded to the rubber tyre/tire.  You often cannot remove the well-adhered patch and do it over.  Your best bet would be to abraid the tyre surface, then push cement into the leak and around the area, WAIT 10 MINUTES, then fit another patch and press it down firmly with a spoon edge or a roller, or a large round coin.

If the patch adhesion is really poor it will peel off in one piece, and you can attempt to buff the tube to remove traces of glue.

If that fails, fit a new tube.   For the cost, its not worth fitting $10 of patches to fix a $10 tube.