You should talk to Capt Keith, because along with a huge list of fears, this was one of my fears (Claustrophobia).
I believe there is a window in the cockpit which will open.
If you have a chance then please go on one of the courses. I had not flown for 35 years and after the course I went on a 4hour flight twice.
It’s now been 2 years and I have been to Australia, Doha and the Far East. Yes I do still gets a bit nervous, but I take the book with me and I always pretend that Capt Keith is flying the plane.