Do i have to wait on my burn to heal in order to used mederma?

Yes: It's not designed for use on an open wound. Wait until things have healed over.

Yes, heal & treat: Wounds need to be healed prior to using scar care creams like mederma. Superficial to mid-dermal burn wounds will usually heal within 2-3 weeks if the wound does not get infected. Infection can make the injury deeper. These wounds will heal with little or minimal scarring if the scar is protected form picking up pigment by exposure to uva/uvb. Deeper burns require specialist care including surgery.