Been in this situation before, have some advice for ya...go to kenny Rogers and do NOT check the score until you get home and GF is in bed. It will make mo difference anyway, other than to make you completely miserable and stressed out all night. You made plans with her, so honor them rather than being a fidgety degenerate all night. There is a certain element and feeling of freedom when you exercise the restraint necessary to just block out the fact that you even made the bet.
Trust me. This is coming from someone who has missed out on a lot of good times bc I was sweating some random game I had a big bet on .
Edit: and my hair has already gone grey at at age 33, so there's that too.