Love the concept. Like Dave L has said though, I think the thought bubble could do with a little more work? Have you tried drawing up loads of bubbles and then swapping them in and seeing what works and what doesn't?
I'm also not sure on the entire width of the C? I'd maybe extend it out a little?
I have made the changes mentioned above to the initial concept, and now all circles in the design are at a ration of 2:1 increasing.
I have also attached a couple of designs where the shape of the c has changed and would appreciate your opinions on what looks right? I am little concerned about the negative/void space that will be created around the design and how text will look next to the mark?