You're pretty new, and I saw too recent reviews. That's not a bad ratio. If you get a couple of reviews a month, that's a pretty good ratio. If you look at the review section, it waxes and wanes for providers.
Don't stress about it
You're doing fine.
If you offer a "review special" that's cool, but personally I do a review if I get a special or not (and I usually don't... in fact, I can't remember the last time I did).
The point of reviews is to share information among clients, but it seems instead of honest reviews, folks want to get something for their reviews. That sort of taints the process. They are not supposed to be "bargained for" advertising, and I don't think that's cool.
My opinion anyway. It's in the same bin as the "no reviews" policy... which I'm not a fan of either.