Have you ever purposely tanked a date?

I went out on a date tonight. Met the girl on-line and she is local. She is a very nice person but I am not attracted what-so-ever to her. Kind of kills it for me because her profile said that she was average and she was much bigger than average. Yes, she was a nice person but I am not attracted to her at all.

During the date I can tell that she is interested in me. Problem is that I am not interested in her so I decided to tactfully attempt to tank the date. I started talking a lot about my ex and tried to do things that I knew would send warning flags up for some people. It didn't work. So I finished the date after dinner and told her that I had a headache (which I did) and that I was going to go home and chill.

Before I get home I get a text message saying she had fun and she enjoyed my company. Why is it that when I like someone and try not to tank it things don't go the way I want them to and when I try to tank the date the girl likes me?

I feel bad about doing this but I just am not interested in this girl. I am probably going to get blasted here because I say that I wasn't attracted to her even though she was nice but I am being honest here, she just didn't catch my eye.

Honestly, have you ever tried to tank a date like I did? How do you handle these things?