I'm a size 20 lady and just got back from DLP. I didn't feel weird about my size just at the park, so it wasn't bad that way. For rides that there were some "difficulties"
-Crush's Coaster: I did have to suck it in to make sure it latched properly. But that ride is so awesome, I'd absolutely recommend going for it! If you can, I'd have someone else take care of the bags. The first time I rode I had a backpack, and it's difficult to fit underneath (the vehicle keeps moving down the walkway as you board and get situated, so you feel a bit of a rush to get settled), so it was wedged between myself and the stranger next to me, but I ended up hanging onto the strap too. The next times I rode I didn't have a bag with me and it was much easier!
-RC Racer: another suck-in because there is the harness above plus a belt that comes up from between your legs. But I got it on. I don't know if they had extenders, but that was doubtful. The ride itself was fun, but not worth a long wait in line.
-RnRC, Hyperspace Mountain, Indiana Jones - typical over the head restraints. Depending on your size in certain areas (chest region), it may require adjusting, but no more so than a typical over the head restraint at WDW.
-Cars 4 Car Rally - now this one was my absolute worst experience at DLP. The seat belts were just too small (like the buckles could touch but not connect). The first CM didn't know what to do. Second CM to check also didn't know what. Finally took a third CM to know there was an extender belt at the front that they could get to connect, but it felt like they made a big show of getting it (like holding it over their head and tossing across the area) and I was the one delaying the whole ride. I was also a solo adult rider, so it looked even weirder because everyone else had kids with them. So I was very very unhappy about that whole experience.
I think those were the only times I even noticed my size making a difference, but overall I went on everything. There were plenty of larger people at the parks (of all nationalities), so it's not like I stood out from the crowd! If anything, I stood out because I was actually polite and followed the rules!
So, I totally get your anxiety (I feel it too), but it should be fine!