Questions & Answers about Ahora me toca a mí.
Because this sentence uses the very common Spanish pattern tocarle a alguien, which means to be someone’s turn or to fall to someone.
So here:
- me = to me
- toca = falls / is assigned / is due
- a mí = to me, with extra emphasis
It is not built like I do X. It is built more like it falls to me or it’s my turn.
That is why yo toco would not work here. Yo toco usually means I touch or I play (an instrument), depending on context.