How to stay positive when you're "the worst person in class"

Has anyone had any experiences with rude or discouraging people in their group fitness classes or does anyone have advice for how to keep a positive attitude and focus on learning and getting fit when you're the "worst person in class" (least experienced and/or least "able")?

I just signed up for a wall climbing class at my gym, which is mostly frequented by hardcore athletes. I am neither a hardcore athlete, nor do I have ANY experience whatsoever wall climbing/rock climbing. I'm really non-competitive, and I don't enjoy activities when I start to feel pressures to compete with others.

The past 2 nights I've gone to the gym late at night to just get a feel for the wall and practice a little before I start class. I have specifically gone after 10 pm so as to avoid crowds, but both times this group of climbers has been there, and they have been downright rude to me for what I assume is just their annoyance that they didn't have the (fairly large) wall all to themselves. For example, last night when I freaked out (I didn't make a huge scene - I just yelled down to my sister that I was scared and felt like I was going to fall for about 15 seconds), 2 of them loudly made a comment about me being "an idiot, abusing the wall." I'm scared other people like them might be in my class and point out my every mistake, or that people in class will act openly annoyed that I'm not catching onto things quickly enough or because I'll be unable to climb or belay as quickly or as well as stronger, more athletic, or more experienced people in class.

Any advice or words of encouragement?

Thanks