The amnio may hurt a lot, I know they say it's only 'uncomfortable', but I thought it was quite painful. Take paracetamol before you come in, it's a kind of deep intense pain. My tum hurt for days afterwards in my case, too.
The worst thing is the doctor told me to grip his arm during the procedure, and I gripped pretty hard it hurt so much, so I'm still worried that I made his arm shake as he poked the needle in! Baby is fine (now 7 months old), but if I had to do it again, I'd grip something else.
I don't know what to say about the worry, if anything can distract you from thinking about it, then do it (like watching a funny movie, whatever). At end of the day, the risk of m/c is still very small. Try to hold onto that thought.
You could look into getting the amnio done privately, one of the fetal medicine centres which officially have same risk of m/c following amnio as rest of NHS, but unofficially their reputation is for much lower m/c rates. It costs a lot to get done privately, though (£450 or so), and I would imagine in your case, you don't want any more delays. Good luck.