Well i know what you are going through, is it the people you are worried about?, the journey its self, or being on a coach or the unknown of what to expect?.
Ask yourself these questions 1 at a time, the first hurdle right getting to the coach area, once you have done that give yourself a big pat on the back, 2nd hurdle getting on the coach do you want to be on your own or sit with someone, sitting with another person is better if you can say hello and start and start chatting the journey will fly by very fast,if you want to sit on your own decide if you want to be at the front which for me is the best you can look at the countryside as you go along.
If you can take something to chew gum or mints something that you like this will help relax you.
And the top thing is have a good time and relax deep breathing is a big big help.
I live every day with this huge problem even shopping is a nightmare for me because i avoid people i hate crowds, my happy place is home in my garden and out on my bike with my labrador Luna.
remember each goal you deal with will give you a huge boost and you will be very proud of yourself.
good luck and have a great time.