Guilt

So today I spent the day with the family and did family stuff. Good day. I added up my calories from my meals and realized that I drank a 700 Calorie milkshake today!!! Say what? I know. Bad decision. Tasty yes, bad for me without a doubt. Instant guilt. No workout today because it's been a family day. More guilt. Why am I feeling guilty though? I feel like I let myself and everyone else down. It's weird I don't understand this. I realize I'm being very difficult on myself I'm just not sure how to get over it. On the upside though I was able to get a beginners Pilates and a starting dvd for yoga tonight. Looking forward to trying those out later and seeing if either of those are exercise routines I wanted to add to my regular mix. Is this whole guilt thing weird or what?