What year, model, engine, etc is the car you're working on? You should fill out your profile with details on your car, or at the least post what kind of car it is so we can give you good advice.

The valve cover gasket is a relatively harmless remove and reinstall job, not much you can hurt. Just tighten the bolts down very lightly, too tight and it will crack. If you haven't found it yet and you're working with a DSM, check www.vfaq.com for help on most basic repairs.