FA's on the 145's now seem to just say, "if it has wheels, it has to be gate checked." So you gate check it, sit, then watch as people come on the plane with soft handle bags, backpacks, and duffle bags larger than yours. If you can cover the wheels somehow, you might make it. Once in a while on a fairly empty flight, I manage to bring a full sized rollerboard on when in row 19 and I have C and D to myself.