You can control the shape of the bowls more precisely by molding the records while they are still pliable. It will probably be helpful to increase the oven temperature to soften the records. You may also find it useful to push or pull on the records while they are still in the oven. But be careful; it is, of course, hot in there.
The can here is being used for weight to help push the record farther into the bowl it is on.
This record was already melted around the outside of a bowl, and now the cans are being used to push the bottom down inside of another bowl.
Placing coins on the record helps control exactly where the vinyl folds. More coins will create more folds. (This doesn't always work perfectly, but sometimes does, so be patient)
After the bowl comes out of the oven there is a little grace period where you can continue molding it to get the exact shape you want. But again, be careful.
Molding a bowl while it's still in the oven.
Uniquely shaped bowls can help create cool record shapes.