You're going to need a bigger pot.
10 gal minimum, bigger would be better.
Unless height is an issue, don't bother supercropping. A tomato cage for support & to spread the branches, should do fine.
Basically tie the top down level with the bottom, it encourages the side branches to grow up more evenly and gives more exposure to the light.
If you hold the bottom of the stem then bend the top part back and forth left to right for a bit it'll soften the stem so it doesn't buckle or break when you pull it down to tie it.