I am sorry but I don't understand why your average score is not at least an "8" if you only had one bad shop but many great shops after that. What do you consider to be high scores and have you had other low scores? For HS Brands, I consider a "9" or a "10" to be high scores, an "8" to be a good score, and anything lower than an "8" a low score.
If you keep doing shops and keep getting high scores, it should not be hard to raise your average to the necessary level.
Let's say you got a "1" for that one failed shop and then get a "10" on 9 shops, you will have a total score of 91 (1 + 10x9) and an average score of "9" (91 points / 10 shops).
If you "only" get a "9" on 9 shops, you will have a total score of 82 (1 + 9x9) and an average score of "8."