Agree entirely with Velvet. For short trips, I often use only a wheeled duffle. It's a bit longer than the usual duffle and easily handles all that I need for an overnight. Early on, I learned that if I wheel it up to the gate, the chances are 50/50 that I'll have to gate check the bag. So I now always use the strap and sling it over my shoulder with the wheels to my back. This duffle fits in the barbie jet bins. I know that for certain, but the GA doesn't want to hear anything about it. I, too, wouldn't engage in a protracted verbal dispute with the GA and certainly wouldn't delay a boarding, but I must admit that I am mightily annoyed when I am forced to gate check luggage that I know will fit. Of course, I don't know that something similar is or isn't the case with the OP. Just sayin'!
lex