Hello suzycaboozy! Welcome to the site!
I'll bet your sponsor would agree that -- to be honest, and to be open, with what's going on for us -- is a couple of the attributes in us -- that determines "who will stay sober and recover -- and who will not."
My suggestion? Have an indepth talk with your sponsor about the problem. My guess is: she was nearly exactly like you -- in regards to this problem. And, she can share with you -- how she dealt with it, and what worked for her and what didn't work for her.
Naturally, you wouldn't want to share confidential information with someone -- that you didn't feel comfortable enough with to -- simply say, "I have a problem with doing this and here is why..."
By speaking up about your concerns you are widening the path of communication between you and your sponsor. You're being true to yourself and true with your sponsor.
In the end, you may not do your 5th with your sponsor or your psychologist... you might do it with some stranger that is so drunk that they can't remember what you told them!
(That was my plan for my 5th: My first thoughts were to share it with a priest... and not my sponsor or anyone else... then, I discovered, that I could share it with some drunk passed out on a park bench -- as long as I was honest!)
I understand your concerns. I had exactly the same concerns regarding my 5th Step -- and, I'll guess, that many of us had the same concern!
Keep coming back!