Bike Fitting?

I have an appointment to get a bike fit this Saturday but it's really expensive.

It seems like the sort of thing you should be able to do yourself, but the only problem is I don't know what I'm doing.  Basically, by the time I get a sore neck or shoulders or whatever, I've been riding like an hour at least.  It just doesn't seem practical to make some adjustments, ride for an hour to see how it works out, and then make some more adjustments, especially since I'm just blindly guessing.

Is it worth paying a lot of money for a bike fit?  I don't even know if the neck and shoulder soreness level is just normal, and the bike fits fine.

This Saturday is my first official team ride with TNT, so I'm looking forward to that.  My mentor Sue said it's 25 miles and there will be some hills, so it sounds pretty doable.  They seem to be pretty good about making sure nobody gets left behind and moving people around til they find the right paced groups, so I'm sure it'll work out.

There is a potluck afterwards and I am supposed to bring protein that does not need to be warmed up, so I don't know what to do here.  Sandwiches count apparently.  I don't know if I'm supposed to buy or make them.  I don't even know how to make food anymore since I started dating Mike.  I guess Mike can make sandwiches.  Problem solved.