Every diet has one free meal or some of them, an entire free day of eating.

It's not that exceptions that will make you fail in the target but the repetition of small bad habits.
Seeing that you have already replaced soda with water is a great start.

And for the walking part, the audio books, the shoes and all the fancy stuffs to simply go walking...well, "done is better than perfect". When you go out to make shopping, start making a longer route than usual. When you go chilling, simply increase the length of the path. Or start today your day1, by simply going out and have a walk around the house or the neighborhood.

Small steps are better than nothing. But you have started doing something for your health, and that's the best part.