This is what I decided about what people think when they see me on a bike.
1) They are amazed.
2) They think about a big woman in their lives (most everyone's got an inactive mom, aunt, sister, daughter, or friend that they worry about sometimes.) (could, of course, be themselves.)
3) They go home and say, "Guess who I saw on a bike today, and she was doing just fine?"

One time I rode by a garden party of older ladies who did triple takes and stared as I went by.

Keep it going, you are doing GREAT!