I do not think so, especially if you have the muscle already. It just requires the proper size horse and maybe add a little extra cushion on their back. I would not do any large scale jumping until you are able to reach closer to 250. Congrats for loosing over a 100lbs!!!! That is some serious dedication and work. Horse back riding can only help :) I do not think that a rider has to be stick thin in order to do jumping by any means. Some chub on a person is completely normal and fine. Be careful with getting back into English though, the stirrup length has your knee at a good angle and that can be troublesome, especially if you have a few extra pounds and are exercising. I would hate to see a knee give out on you when you are doing so awesome! Maybe wear some knee braces while you ride for now and keep then as long as you comfortably and safely can.
Awesome that you have lost that much so far. Absolutely do not be embarrassed! Riding is helping me drop some pounds. For me yoga focused on core has helped me and helped my riding. Keep it up girlfriend and keep on advancing your riding skills!!
if you are overweight and want to ride simply go on a weight loss plan. exercise & eat right. my grandma went on the "eat right 4 your type" diet & lost over 50lbs easy. it's not expensive and it's easy to do