Is 30 better then nothing?

When I exercise I like to do at least 45 minutes. I know in the past I have said I have to do at least 20 minutes of exercise but I hardly ever do only 20. I don't know why I have this mentality that if I only do a little it is not enough, but I know a little is better then nothing. So last night I got home from work to find out we have been invited to a friends to watch the game & get pizza. Now I love, love , love pizza. So I was in (even though I have to weigh in tomorrow & I had not exercised yet other then a 10 min walk with the dog). I went saying to my self I will only have 3 pieces at the most. Well that went to hell. The slices were really small & I ended up eating 6 pieces, some Tostitos chips & a pudding (fat free) parfait. I felt like crap after eating all that, not because I was full, because believe it or not I did not even fell full, but because I eat so much & I had not exercised. I felt bad but not bad enough to have bad thoughts in my head. Well I screwed up I might as well go home & eat more crap. Then the mind starts in on what do I have at home that I can have? Should I stop at the store? So I left, on my way home I had a reality check. No you will not stop at the store you will go home & get your but on the treadmill. So instead of eating more when I got home I did the treadmill for 30 minutes so yes 30 is defiantly better then nothing in more then one way. I think I might try that, when I have bad thoughts to get up & do some exercise & push the thoughts out of my head.