You're not being ungreatful, you're maybe just upset even if you don't exactly know why at the time, I have days like that, I go somewhere, have fun yet Im so anxious or pissed that I feel bad because it is suposed to be a good day and Im not exactly having as much fun as I could, and feel that others notice it and are upset with me, but idk why I feel that way at the time and may not even know until hours or a day or 2 later why I felt that way. But don't feel ungreatful for how you feel, you're trying to have fun and be yourself.