Hello, Im in high-school and I also have that stutter you're talking about. With me is I can say those words but there's a 3 second delay and it's really frustrating especially bcs when I'm alone I can say those words just fine but in class I can't. A qualified person told me I don't have the traditional stutter just the fear of stuttering makes me stutter. So I'd say don't think about and talk more in the mirror or to close family or friends. If that doesn't work repeat the word or sentence 3 times in your head. That sometimes works for me aswell. I'm younger then you but just try not to think about it.