I need to get into shape but what sport would be good......?

Ok so im like realllly out of shape. I'm 13 and about 104 pounds and my legs and arms are like twigs but my tummy is reallly fat and flabby and i have like 6 folds and its just really frustrating. I cant even touch my toes, do a pushup on the floor, or not even 1 cartwheel. I know i need to get into shape but i dont like being forced to go to practice or go to games. Its just not my thing at all. I dont know how to get motivated to just exercise. I just want to be healthy again. I used to play soccer but now i feel really uncomfortable playing a sport. We have a gym at our apartments so how fast and for how long would i have to go on the treadmill for results. I can do like 30 wall push ups btw. PLEASE HELP