Mine did the same thing, brand new right out of the box. I contacted Rotatrim in England and they sent me out a new cutting head and that did the trick.
I wish I knew that. I wouldn't expect something out of the box to perform so poorly, so I assumed that's the best it can perform, and now it's too late to ask for a replacement.
I did note that in Chapter 15 of the 'Luminous Landscape Camera to Print & Screen' tutorial, just published, Michael comments that his Rotatrim (which appears to be a Professional model) cuts only in one direction and has an arrow to show the direction - I wonder if it applies to your trimmer.
It does. you can use the cutter swiping from right to left only, though mine doesn't have an arrow on it. still, this is too much hardship to expect from a professional cutter.