Hello, Fernando. The phrases, "may have" and "might have," are used to express past possibilities. You can say, "I may not have turned on the oven," or "I might not have turned on the oven." Either sentence works because "may have" and "might have" are interchangeable. Sincerely, Ryan

I possibly have not turned on the oven or I may not have turned on the oven. May and possibly mean the same thing in this sentence so you don't need to use both

I would not use 'possibly' in that sentence. the word "may" implies "possibly". I would say. I may have not turned on the oven. More naturally for me, personally. "I probably did not turn on the oven."