Who says girls like boys who love sports? What's wrong with being gentle? Much better than those boys with developed limbs and simple minds.
I think boys who like painting are very literary and your height is just right. There is no need to change. It is the most beautiful to show your true self.
PS: If you feel thin, you should always go to the gym to exercise. Over time, your figure will be better, which is good for your health. That would be perfect.