We sympathize with your predicament. Nobody wants their image used for purposes of commercial endorsement without consent. The purpose of a release -- assuming its drafted properly -- is to grant consent. We think that you're in a tough spot and may be bound by the terms of the release. Most courts consider a written agreement as the "final" statement on the deal and your release may even have a clause entitled "Entire Agreement" or "Integration" that guarantees this result. The fact that you didn't read the release (or were advised not to bother) does not excuse you from the obligation.
Duress? You also imply duress -- that you were pressured to sign. In a sense you describe a form of economic duress. That is, you'd lose your livelihood if you objected. But to prevail on a "duress" argument under contract law, you would likely need more evidence of physical or mental coercion to demonstrate that your consent was not voluntary.
Consideration. As for additional consideration to sign the agreement, that's a tough call and may depend on your state law. In some states, such as Pennsylvania, additional consideration by at-will employees may be required for certain agreements. In other states, like Wyoming, Colorado, and Ohio, it may not be required for contracts that establish non-competes (that is, keeping your job is sufficient consideration). (We're also not sure how much of this legal minutiae matters as we're assuming you don't want to take this matter to court.)
You're so pretty. We find your boss's comments about your appearance, such as "you're so pretty," as troubling but by itself, not enough to form the basis for a lawsuit.
For more information on using employee photos in social media, you may want to check out this blog post by one of our favorite employment law experts.