Paying for an ad...should I? shouldn't I?

I've made tremendous strides with Girls Life magazine and I'm close to a deal that would put the books in both their online magazine and their hard copy for a couple of months, plus they agree to add a Facebook and twitter campaign to sweeten the deal. Sent junior year off for editing, mailed off a giveaway to a delightful girl in Ky and sent off a Kindle version. What a difference a day makes. Last night I was feeling overwhelmed and wondering if its worth it. Now I realize they're are going to be good days and bad in the world of marketing. I'm working on the book jacket description for junior year and have a case of writers block. Still shooting for that end of the year deadline.