I was told my unborn baby has a 1:120 chance of trisomy 21. i am doing more testing, but how concerned should i be that my baby has down syndrome?

Hard to not worry: This is a very anxiety provoking test in many cases. Remember this - it is only a screen. This means that there are a large number of false-positives. This is designed this way so that we don't miss the babies that are actually affect with down's. The additonal testing will help greatly in terms of what is going on. The odds are still very much in favor of an unaffected fetus.

Glass half empty ?: You can also look at this as a 98+% chance you don't. Any pregnancy has about 4% chance of some unexpected outcome, including prematurity, birth defect, sick baby, etc. If you're like most moms you worry about stuff like this happening anyway, it was just brought into focus by the comment. Hang in there and try to enjoy the idea you will likely have no problems.