Why dont the presents shape of the continents fit perfectly in to a supercontinent?

They do I did this topic in school with my teacher and she said all continents do but North America did have Florida back then

They still do, but if they didn't it would be the cause of weathering and erosion. These factors can later cause the shapes of our continents and it could no longer be able to form this supercontinent known as pagea. For right now they are still in stable conditions, and it would be years before they are eroded and weathered to where there forms change.