Review the original item:
Wally did not want to ruin his new pair of athletic
shoes,
he always stayed on the sidewalks, sidestepped puddles, and made
several trips a day to the bathroom to wipe the sneakers with toilet paper.
You chose the correct way to fix the error:
Wally did not want to ruin his new pair of athletic
shoes,
so he always stayed on the sidewalks, sidestepped puddles, and made
several trips a day to the bathroom to wipe the sneakers with toilet paper.
A perfectly legal move in writing is using a comma and coordinating conjunction like so to connect two main clauses.
So shows result; thus, it works perfectly in the example above.