jachym michal is right, run a seam along the top circle of the cup to separate the interior from exterior, also along the circle of the bottom. It looks like you have a seam running up the side, make sure it runs down the interior too. Basically, think of it as an orange you have cut in half, you have two half balls and you can't just lay them flat, you need to make a cut somewhere to let it open up. I'd also run a seam along the inside edge of the handle. Think of the handle like a tube, you can't spread it out but, if you slice it longways you can unfold it nicely. You may not need to run a seam along the bottom of the cup, it looks like it may converge in a point and the side seam will take care of it.