My boss emailed me and told me I did the timesheet wrong.

I told her I'd be in Monday (today), but I just got an email saying that she had to turn in the time sheets already, implying that I caused a major inconvenience because I didn't bother to pay attention to the time sheet.

I'm afraid to go into work today. I'm such a stupid f***-up, and I know my boss thinks the worst of me. She thinks I'm blowing off my job because I'm busy with the practicum.

I keep trying to do everything right, but then I do something stupid and mess it all up. What is wrong with me, that I continue being a stupid f***-up? How can I force myself to do my job right?