My son did a projectile spit up, what should I do?

He was born 10-21-2008 and was 6 lbs 7 ozs. when he was born. He was 6 lbs 1 ozs when we were discharged from the hospital. He is now at 6lbs 3ozs. But lost an 1 1/2 ozs. since saturday. The pediatrician has me supplementing him with formula. He just projectile spit up on me and it was probably 2 cups, if I had to measure it. What should I do?