For this cake, I split a cake mix between a 9" round pan and a small heart pan. An 8" round pan would work fine if you don't have a heart pan.
I bought purple Pillsbury frosting and made my own teal frosting with blue, green, and red food gel. I just used a small star tip to create the border and the little star bursts around the cake. I did add some of the purple, blue, and black sprinkles that came with the frosting, although it looked cute without them too. Then I added the little Doc figures my daughter had from the Disney store.