Bad ergonomics...and a bad grade

What am I doing wrong at my desk(s) that makes my shoulders feel tense all the time? Maybe I should do more lat exercises or something. I'd really like one of those expensive chairs from Sharper Image. :-) I'm doing awful in my Spreadsheet Applications class. I never dreamed spreadsheets would be so difficult. I've done the simple things with them since middle school. I've got an exam coming up next week over pivot tables. I've really got to pull through and get an outstanding grade on this one. I do not want to have to take this class over! The assignments that were due today were kind of tough. I emailed everyone in the class for some help. I got two replies, but they weren't of much help. One volunteered to take a look at my work tomorrow. It had to be turned in today!