Yes, definitely tell people. This will help. Of course they can hear it (tho some might not know what it is), but being open about it automatically makes it less of a big deal for you and everyone, you know? I've never used a pallet jack, but I'm pretty sure I'd suck at it too at first. You will get it. Severe (crippling) social anxiety is.....brutal. I really hope that finding some confidence and sense of accomplishment at this job helps some. Doing this is very brave of you and I wish you all the best in the world.