"Good" or "Bad"

I need to stop thinking of myself as being "good" or "bad" based on my food choices for a day.  I ate relatively well yesterday but went out to lunch with friends at work and had a grilled cheese sandwich and chips (not the best choice).  Other than that, I ate only healthy foods (e.g., greek yogurt, fruit, protein shake, salad for dinner), and I worked out (3.5 miles on the treadmill at a 6.3 pace and weight machines for arms). So, when I look at my day, why do I think "I was bad yesterday."?  Making the wrong choices for one meal doesn't make me a "bad" person. This mentality is bringing me down and I need to stop!! 

I am looking into the paleo diet, but I don't want to think of it as a "diet," so I need to do some more research to see if I think I'll truly be able to make it a lifestyle.  I'm tired of always worrying about what I'm eating and I'd like it to just become a natural way of life for me. I haven't found anything that's worked yet.....maybe this will be it?