Hi ((((((BatsandButterflies)))))))))

I'm sorry you are stressing so much about this. I can definitely relate. I have developed a phobia of flying and I can start feeling anxious just by thinking about being on a plane. I'm so sorry you are also dealing with an intense fear of shots.
Are you taking anything for anxiety? I am not personally a fan of anti-anxiety medication for a number of reasons, but sometimes there's just nothing else for it! There are also some natural calming remedies that help some people. I also use things like essential oils (lavender) and I try and do my breathing exercises. Sometimes it can be helpful to listen to a calming CD as well.
I'm not sure if you're seeing a therapist or not, but this is definitely something that a therapist/counselor could help with.
I really feel for you because I know how bad phobias are, but I think it's GREAT, REALLY GREAT!!! that you are planning on going on this trip in spite of your fears (and even though you have some doubts, it really does sound as though you are going to go. Which is absolutely the right thing to do!!!!) You will feel SO GOOD about yourself for doing it!! Try and focus on that too (on how good you will feel afterwards). But definitely, it would be a good idea to get some additional professional help beforehand also.
Good luck!!!!!!! And let us know how it's all going