You probably have a little bit of squareness adjustment in the rail (where it clamps to the tabletop) - slacken off, move until fence is parallel to the blade, re-tighten. I don't remember that the rail clamp itself has anything to allow fine adjustment.
To make a rip fence from a long rail, as I said, just apply some flat, parallel stuff the the face of the fence as far as the front edge of the blade and not much further - voila! short fence (and one that doesn't move about, too). There are T-slots n the fence profile too, so you can attach the short fence add-on to the main one fairly easily too.
But do the whole thing in the right order:
1. align blade to mitre track by adjusting the trunnion clamps fore and aft of the blade. This is a right PITA to do on the early versions, but you only ever need to do it once (probably!);
2. align fence/rail to mitre track.
In both cases you want exactly parallel, and ideally you need a dial gauge or similar to measure it. At a pinch you might use steel bar and feeler gauges, but that's not easy.
E.