Once a bracket/entry is created it cannot be deleted. It can be renamed and you can edit the entry settings or change your picks before the tournament starts but it cannot be removed.
There is no penalty for not filling-out all of your created brackets/entries with team selections or using them to enter into a group.
If you have erroneously created a bracket, you can simply ignore it until the NCAA Tournaments are over and all brackets will be removed.
Best of luck with your selections!