When I was a volunteer at the SPCA, I did that several times. I can't remember the type of dog but I just remember there were other dogs I felt more connected too and would rather walk. So I would walk the other dogs and hope that somebody else walked the dog I really didn't want to walk. Sometimes it worked and sometimes it didn't. So I ended up walking the dog I wanted to walk and the dog I didn't want to walk.

I wouldn't worry about it.

The fact is, you are volunteering and making this world a better place. Volunteers are special people. I should know - one of my jobs is volunteer coordinator!