How do you combine multiple faces?

Hello, I’m trying to do split body, but the plane I drew has multiple faces:

Because of this, when I do split body, it’s not following the full contour of the shape, since I can only select one face at a time.

How can I combine these faces into 1?

Just to let you know, the sketch itself it also not one smooth curve. I created this sketch by using the project function.