Gyms are so unwelcoming and fatphobic and they don't even realize how out of touch this makes them in this era. I live in the UK so fully expected my similar to yours gym experience (like you I joined a gym after shunning diet culture once and for all, which motivated me to move my body how I wanted to). If only the fitness industry could catch up to the fact self love/acceptance is a much bigger motivator than self loathing. They stick at promoting diet culture which is a failed business model and results in most people quitting after a couple months. Well done for standing up for yourself, I know it's not easy in that environment.