Before you beat yourself up, what did you start with? If you started with $50 and left with $100 I'd say you did fine. If you started with $90 and left with $100 you still did well. And if you started with $100 and left with $100 you beat the casino because you also accumulated slot club benefits (provided you played with a card).
Let me add to this: on one of my recent trips to Rincon I had $290 of free play. In the early going I got very lucky and had $900 on the meter playing $1 Aces and Faces. Then I started losing. I left with $240 cash. I considered that to be a perfect score -- only used free play and left with $240 more than I came with.
I don't regret not cashing out at $900 because I gave myself a chance to win more.