It's tempting to rush through the last steps after taking your pineapple upside-down cake out of the oven. For best results, you must wait for all of the ingredients on the bottom of the pan to settle into the cake. This could take up to 30 minutes. If you don't wait for it to settle, the bottom ingredients will spill all over the place when you flip it. You also need to make sure you don't leave the cake to cool down for too long, as the bottom of the cake tin is sticky and may stick to the sides of the pan, making it harder for you to get it flipped without making a mess!