You have to do what you feel is best. I guess I would stick it out with the fiddle group being you already paid and they are not being judgmental.  The ensemble class is another matter.  Learning to play or playing in a group does not have to be an intimidating experience. If they allow different people to join at different skill levels and don't require auditions then they shouldn't be judgmental, make people feel uncomfortable, or make people feel unwelcome. It certainly isn't going to help build your confidence and skill if you are treated harshly and made to feel unwelcome. Certainly an instructor should know better. You might want to consider dumping the ensemble group and just sticking with the fiddle group for now. Perhaps at a later date you can join a community orchestra or local ensemble that is more accommodating and non-judgmental.

BTW as a child in the mid 1960's my first violin instructor (an accomplished musician himself) was a rather harsh "old school" type who's temper would flare and would swear like a sailor if he felt you weren't practicing enough and/or he wasn't satisfied with your playing.  It made my earliest learning experiences and group playing experiences somewhat frightening and I often found myself practicing and learning out of fear of being reprimanded and hollered at at our next group lesson (we learned in small groups of 3 to 5 young pupils). Going to lessons was scary as heck for me because I was so scared of being hollered at that I knew I would end up making mistakes out of fear and then definitely get the teacher riled up and get yelled at. And trust me, I did get yelled at. Every lesson was like constant stage fright... a real nightmare... While I stuck with it and I did learn to play it was still a frightening and intimidating experience all of the time. Later on when I studied under other instructors I realized there was no reason for that type of harsh intimidating approach to teaching music.