Not an easy angle for a portrait and the fact that your photo is not straight on skews the perspective. A really really good attempt. There is nothing harder to figure out than skin tones and that is why so many artists avoid it like the plague. Keep at it, you obviously have some feel for pastels or you would not have been able to make this.
When painting I had read that red violet was the secret ingredient for puffling life into the skin, hard to find but well worth the search. I used it on my assignement. I don't know what answer that is for pastels. You also want to add a little blue or such into your shadows for your skin. It takes such a minute miniscule, partical, dram, speck of it, but it is necessary. Not grey. A guy painted my portrait in our Illustration class at the tute and he used some grey and was chewed out royally.
If your going to pursue this, the library should have some good books to help you along the way. Ours has the watercolor bible, the Glaze Bible..and so on. All are priceless in the secrets they contain.