I'm no expert here, but I think spinters can hit over 40 at the finish (I know I used to do that during club training loops), can you? On a flat course, I don't think 19.5-20.5 is going to cut it. Can you ride in a pack and are you comfortable bumping into other riders? Take the advise of Mr. Laggard and find a fast group ride and see if you can hang with them.
Good Luck.