People tend to overestimate the amount of calories they can burn through increased activity or exercise.

Walking a mile will burn about 100 calories, give or take. That's not much. A latte from Starbucks or a "healthy" snack such as a granola bar has more.

Good rule of thumb is that you cannot offset a bad diet with exercise for weight loss. Diet is by far more impactful. Exercise has other benefits though, which I'm not intending to dismiss.