Third degree burn on chest,was told i had cellulitis, put on oral antibiotic but lab culture smear results negative, suggested burn scrape.do i need?

Physical findings: Surface smears of a cellulitis usually do not grow the causative organism. Sorry about your burn. If there's a reasonable suspicion that the burn is infected, an antibiotic is appropriate. Best wishes.

Not enough: Not enough information. Are you really sure it is 3rd degree??? How? When? Treatment before antibiotic? Was some topical preparation or antiseptic used before the culture? What is a "burn scrape"? Most diagnoses of "cellulitis" by amateurs [non-dermatologists] are wrong. You failed to name the "oral antibiotic". If in doubt, get a second opinion, preferably from a dermatologist.