you kept it, the 49+49+1=99 is how much you owe mixed with what you still have, the riddle changes context halfway through so the math doesn't function correctly
2/10 took me <20 seconds to figure out
idiots guide:
after spending 97, you have 3 left and owe 100
you give one back to each parent, so you owe 98 and keep the last dollar
you still spent 97 on the game and gave 2 back to your parents, so you have the last dollar