If there are illos. in the book and your work is only on the cover, then nothing is wrong here. I hope you at least got paid for this. BTW, if you want you work to be used on ANYTHING, make sure you approve how it is handled. If you don't like the way the text was going to be used on it, then say somthing!
IMHOP, if you are not proud of this book, then I wouldn't even show it off. Just chalk it up as a learning experience. Do you really want your art to be associated with crap?
"If one advances confidently in the direction of
his dreams, and endeavors to live the life he
has imagined, he will meet with a success
unexpected in common hours."
- H.D. Thoreau