Are you brewing from a kit? They probably gave you too much sugar. Try and estimate the actual volume of beer you'll bottle (accounting for yeast/trub you'll be leaving in the bottom of your fermentor) and punch it into a bottling sugar calculator.
If you just dump in the whole 4.5 or 5 oz, your first beer will be all gushers like mine was.
...and, of course, congrats!