Stuck gas door???

So, my gas door won’t open. It did this once last week. I thought it was because I had the key in the car. I took the key out and eventually it popped open. Today I pull up to Costco and it won’t open at all. Sat there for 5 minutes playing with the locks and pushing the hell out of the door. Still won’t open. I can’t get it serviced until later this week. Does anybody know what this is and can I fix it at home? Model: 21 K5 gtLine