I think it will be a shame for you to pull on Friday due to a weather forecast. Or actually multiple forecasts because as it is 100 miles, it can be quite easily dry in one place but tipping it down in another. Lets say on Friday the weather is dry for Sunday but rain on Monday so you decide to do it. The wind picks up on Saturday and the rain arrives early on Sunday. Will you do it or pull out?
Last year was my first sportive and so I had never ridden with others. Yet I was put with over 10,000 other cyclists, some in the same boat (excuse the pun
), with the aftermath of a hurricane added to the mix and do you think I was confident?
You've said you don't like riding in groups, yet you've entered an event with 24,999 other cyclists so dry or wet, you'll automatically gain confidence there. So your already going against one of your worries without probably even thinking about it
Us humans can do things if we put our mind to it and conquer things so even if it is raining, you would probably still get around