Yeah, those clubs will definitely help you out. With math olympiad, I suggest you put in dozens of hours if needed, and win some awards. That will be something that will boost you right up. The student life sector of TAMS is heavily emphasized, so definitely try and show them you can contribute through clubs or whatever.
As for credits, unless you stay at UNT, there’s a very low chance all your credits will transfer unless you go to a school around the same level as UTD in state. However, with some luck even out of state colleges will skip you through some classes based on credits. Don’t count on it though.