Sounds like you are doing great.

After riding an hour or more, I always eat something soon after. I don't buy fancy recovery drinks, I just eat something sensible like a sandwich, a bowl of cereal, or bagel with peanut butter, etc.

12 weeks should be plenty of time. After a long Saturday ride, try doing a recovery ride the next day. Don't worry about speed, and just try a few miles the first time. After you get warmed up, you may be surprised how you feel. I was. I usually cannot go all out the next day after a big ride, but it actually feels good to get out and get the legs moving. I often take my kids on the recovery rides, that helps me just do a nice casual ride.

Are you eating and drinking good on your longer rides? Once I got above 30 miles, getting the right fluids and calories at the right time became much more important. I plan on one 24oz bottle of fluid per hour (more in extreme heat), and a gel pack or equivelant every 45 minutes.

Leading up to your ride, for my first century I tapered back the intensity of my rides starting abour a week before, and took 2 days completely off before the ride.