However, it’s worth mentioning that your fuel tank door will not open unless your vehicle is unlocked. When your car doors lock, your fuel door does, too. This is to prevent gas tank tampering, siphoning, or other mischief by unknown parties.
If you’ve already unblocked your car and pushed on your fuel tank door to no avail, however, it’s best to visit the mechanic. It’s possible that there’s an issue with the door locking mechanism, and you want to drive to the mechanic before you run out of gas and need a tow instead!