At those settings, you have about 0.8 inch of depth of field on either side of the point of focus (http://www.dofmaster.com/dofjs.html). That should be enough (barely), assuming you have the focus spot on and nothing moved.
I agree with Grahame: it looks like you might have missed the focus slightly, as some other parts of the image are sharper.
Most lenses are less sharp when wide open, and that will probably be more so with a budget lens, which that is. I had a copy of that lens for a while, and it could get nice, crisp images if stopped down a few stops.
I would get rid of the polarizer. I don't see a need for one in this photo, and it is robbing you of a few stops of light that you could better use by closing down the aperture or increasing the shutter speed. Also, if there really is backlighting, filters can cause flare and ghosting, particular inexpensive filters, if that is what you are using. Try it without the filter to see.