As others have pointed out you have already started a riding program. It does not have to have structure at this point, it only needs regularity and that can be whatever you can spare. It's like putting one foot after another and before you know it you got somewhere.

Your first ride was longer than my first ride. I agree with your assessment that you can't just follow someone around on a bike. Once your bike fits you comfortably sit back and enjoy the ride and notice things around you and your neighboorhood that you never noticed driving by in a car. Sounds corny but smell the flowers and immerse yourself in the joy of outdoors and before you know it you will eagerly look forward to getting out for a little bit as often as you can.

Many happy miles to you and congratulations for taking that very hard first step by getting off the couch and getting outdoors and active!