At 21 you are still developing. I had several abnormal paps before I was 22 and even had biopsies done and nothing came out of them, the specialist told me that its very common for young developing women to have abnormal results. Just follow up as your doctor directs, but I wouldn't worry too much about it
There are a lot of reasons for why a pap may come abnormal, but it doesn't necessarily mean something is wrong. An infection can cause abnormal results along with other possibilities.