Gas tank says it's full but I know it's not

I had less than half a tank and went to fill up before a long drive. At the gas station, the pump wouldn't let me put any gas in the tank - it kept clicking stop. I gave up and was going to try again later, however when I turned my car back on, it said I had a full tank all of a sudden. The gauge on my dashboard isn't going down at the right speed either.



Has anyone else had issues like this, or is this something I'll have to take to a dealer to look at?