Hi there Heather
The gals here have given you some good starting points for starting to ride in groups.
Just want to emphasis again what has already been said: let the others know this is your first bunch ride.
There will be someone there who will give you tips, encourage you and if you drop back will come back with you and support you back to the group or sit at the back of the bunch with you.
The only way to really know is to have a go, just have a go and be open to suggestions and opinions Come back and talk to us about how you found it - we'll be interested to talk with you about it.