Current Job

I'm one month into my new job and it is OK.  I'm stressed about making mistakes and the time card system drives me nuts.  It is set up on 100 ticks but I've got to get that I've got to be sure I'm working on 15 minutes which is 25 on their system and work it out so I don't get overtime.  I ran over 15 minutes Friday,  I thought I was leaving 15 minutes early, so I'm really stressed I'm going to get into trouble.  They are very tough on the rules on this job,  I emailed my boss and asked if she could change my time stamp.  I really didn't want the OT, I was ready to go, I was working on a spreadsheet with the 51 bills I got in on Friday.  I was busy 3 1/2 days last week out of 5.  I'm hoping I have enough work that they don't want to take me down to part time.  I need to not work so hard or fast,  I always seem to have this problem with my jobs.    Why do I have such a hard time with mistakes.  I can take this farther into my life and see where that is a lot of my heartache comes from.  Oh well I'll take my beating on Monday and get through it.