In the past year, I paid membership dues to a JCC (similar to a YMCA), which is a non-profit, charitable organization. As a member, I am entitled to use the gym at the JCC. Would this be considered a charitable donation, or would it not qualify since I a

It's very unlikely that the dues are deductible.  According to the IRS:

You may be able to deduct membership fees or dues you pay to a qualified organization. However, you can deduct only the amount that is more than the value of the benefits you receive.  You can't deduct dues, fees, or assessments paid to country clubs and other social organizations.

It's likely that the value of the gym membership and other facilities available to you as a member equals or exceeds your membership dues.