Hey TA.....I think what happened is that you're waiting for the rest of the field to finish. That way, they know how much prize money to give out. Basically, you crossed the finish line and need to wait for them to catch up. The prize money screen will come up automatically.
ALSO: And this is VERY important.....When you cash in your credits from b-specing, you MUST save immediately. Otherwise, when you shut off the PS3, you'll loose the money/credits you got.
There's been a couple updates to the game since they discovered this "bug", but I'm not sure if they fixed this yet. Better safe then sorry.....just click the little red dot thingy.
Bob