Question: Measles, mumps, and rubella vaccine …safe to repeat shots

My college told me that I need to get a(n) MMR booster shot. They said I received my first and second dose of MMR too close together back in 2002. Im not sure if I actually ever got my second dose of MMR, but I know I got the first one. Is it safe to get the MMR booster shot having only had one dose or already having both doses even though Im not sure if I’ve had them or not. I called a pharmacy and they said they can give me the shot. I just want to make sure if it’s ok. I’m 20 now if that makes a difference and I received my first dose back in 2002. Thanks