Can admin change this to a positive?
You can't go neutral for not getting services the WG doesn't provide!
I tend to agree, but it's OP's review and it's OPs rating. End of.
If he reflects and wants it changed then he either posts that request here or reports his own review with a request to change.
However, if he's happy with the rating as it is, then so be it.
Of course, if you feel really strongly about it, you could report the review for Admin's attention. However, the likely outcome there is you will get slated, called a WK, and the current rating will continue to stand.