Out of all the choices you would have been given, you chose merperson, which was something you were actually going to have a hard time with, because fusing limbs was going to be a major struggle while you were underwater. Still, you felt that once you became a merperson, you might be better at swimming.
As a child, your parents always took you to swimming classes, but you were having a hard time completing them as the other kids always won against you, while you started to drown at the community pool, and almost die. The last time that happened, you had to get some water pumped out of your body to stay alive from that. Luckily, once the other students paint, draw, or sculpt you as a merperson, you would be able to swim around the water as if you were meant to be a fish.