WHAT YEAR IS YOUR BIKE????????????????????????????
KEY IS NOT TURNING:
Try the hair dryer method again but this time use a penetrating oil. Squirt some into keyhole. Let it "penetrate" (that's what she said) for a few minutes and try. If not, then blast it with the hair dryer and then try again. Consider repeating.
Also check your key for deformities, consider getting a new one. Maybe its not lining up the tumblers properly.
KEY IS TURNING:
Push down on the cap before pulling up.
Check your vacuum hoses, make sure they aren't clogged or pinched. Had this problem before where gas cap was hard to open because of the gas tank becoming a vacuum because it wasn't venting properly.
Finally, take tank completely off and try to access it from the bottom to include taking fuel pump off. If its some sort of vacuum issue, this would alleviate it as well.