Work Issues

Work Issues i work in fast food and have been for about 6 months now. I’ve learned everything except front counter and back window/coordinating. I’ve asked my boss several times if i could get trained for those positions. He said i needed to learn how to do sandwiches. ( I learned it last month. I’m fine at it.) Everyone knows I have a stutter. Especially my boss. I’m feeling like he doesn’t want to have me learn the new positions/ones i need to do, because my stutter could get in the way of reciting orders back to customers. Every time I want to ask him if that’s why I haven’t been trained how to do it, I get anxiety about it and don’t try. Any advice? Thanks loves.