Mel, that sounds like a good plan with the mid-week training.

On the long rides, are you doing okay with nutrition and hydration?
Remember to eat at least 100 calories every half hour, with plenty of water. On my first century, there was one point where I just didn't want to eat, and knew that was probably when I most needed it, so I choked down a gel. I felt better after that.

You want to be really comfortable with what works with your system on a long ride before the big day- no surprises!