As was stated by the others there are some factors the sims don't present you with. I would have some friends come over to help you get ready for the real thing.....

Have one friend talk in your ear like you'll get at the field when someone comes over while your flying. Then have them wave thier hand in front of your face to simulate someone walking in front of you to retrieve thier plane (poor field ettiquite). Now for the pucker factor that Minn mentioned....have one of them stand on a table over your plane with instructions to jump on it if you crash.

On a serious note....stand up while you fly the sim as you would at the field. Do you live in Los Angeles near the Basin? I'd be happy to help you out for a couple of lessons because after the sim practice that's all it usually takes before someone can solo. You don't get the perspective of the real thing from the sim to be able to line up with the run way, especially if there are other people flying which will make you nervous. The learning curve is dramitically shorter though having practiced like you have. Good luck!