I agree 100% with your sponsor. My concerns at that point were "how can I turn my will and life over to something I don't know?". My sponsor told me at step 3 I didn't turn anything over, I just made a decision to do so.
I read this somewhere: 3 frogs are sitting on a log and one makes a decision to jump off. How many frogs are on the log? 3. The last frog hasn't actually jumped yet, he has just decided to jump.
In step 3 you decide to turn you will and life over to the care of God as you understand Him. Turning it over comes in working the rest of the steps. Your understanding of yourself, your addiction and your HP will be profoundly different at steps 9 thru 12 than it is now.
This is what my sponsor told me, and it turned out to be true for me. This was one of the hardest steps for me to grasp, and this approach really helped me.