Would my exwife be entitled to part of my retirement after only being married for 7 years?

You may need to take your dissolution (divorce) judgment back to an experienced family law attorney and have him or her review it. Depending on how carefully and completely the original judgment was done, it may be easier or harder to figure out what your ex is entitled to, and how to get the plan administrator to release the rest to you.

As you've described it, you put in a number of service years during the marriage, at a time when none of the returement was vested or vesting; now it's vested. She's probably entitled to some portion, though it may not be much.