Walking is typically very good (and often suggested) as a way of bringing BG down, so if you're walking immediately after eating you could try reducing your bolus dose, or even taking it after the walk - the difficultly is that your food may (will probably) take more than the 20min to be digested so you'll still need some (more) bolus after you get back from the walk. If I ride at lunchtime I will eat uncovered and then correct when I get home though if I'm running towards the top end or high, I'll probably take a unit or two so there's something in my system (and be prepared to eat a snack if I mis-judged it, c'est la vie.)
Obsessing over numbers is one of the downsides of CGMs and overcorrecting is a thing that happens in many walks of life as the body (or whatever other system) doesn't react as fast as your brain wants it to!
I sometimes do this too, though I rather try to learn from what I did (how much bolus, how long before eating, what was the effect) and then do something different next time rather than trying to correct and potentially end up with oscillations.
What do you use to see how much IoB you have (e.g. XDrip+ does this quite well)?