I certainly didn't know I was going solo until my instructor took control and taxied off the runway - I hadn't thought about it that much up until that point!
That was almost three years ago and this afternoon I sent of my application to the CAA having completed the skills test yesterday afternoon.
My first solo has been one of the highlights of my flying so far. My advice would be to relax and enjoy it. The fact that your instructor thinks you can solo is a compliment to your abilities so far...