Yes, I agree with the above post about the upB. Its usually great for a surprise kill move, but since you spammed it, it lost its ko potential and its put you at risk every time. I would say to try RARing a bair instead. The tipper has great knockback and could have definitely killed peach faster than the spammed upB's. Also the dancing blade works really well with the up combo like 3xSwords said.
Also, i though you could have incorporated Marth's grab game a lot more. Instead of doing a nair and retreating, try a fast falled fair to forward grab (he doesnt have a lot of range but its still really fast and useful), then that tippered nair out of the grab will either kill or set you up in a great edgeguarding position