Why dont the present shapes of the continents fit perfectly into a supercontinent

They dont fit together because they arent shaped the same way as each other

Sometimes as the continents drifted apart, they sometimes broke off a small plot of land, and the broken off land will make the spot it broke from shaped differentl around the edge of where the small plot once was. The continents could fit together only if the plot was in its original location during the breaking of the supercontinent. Hopefully mu explanation mad sense to you.