Calendar Not Working....Please Help!!!

Just got my Droid and was seeing how everything works. Selected the calendar app., selected a day and said I was working. Everything worked. The problem is when I tried to erase it. After I erased it, it still shows I'm doing something that day. I've tried clearing the data through the filter and I also tried data synchronization settings. Everything is how I believe it is supposed to be, but my calendar still won't erase the day. PLEASE HELP!!!!