When loading the film, after you line-up the film's double arrow with the cartridge's red triangle, and loading the cartridge into the back casing... did you wind the film-back (clockwise, if you're looking at the counter window) until the knob stops? Sounds like you missed this step, from your description of the problem. This initial winding sets the film inside the back to the ready position. You can turn the knob counter-clockwise afterwards to have the handle sitting out of the way.
Do not turn the knob clockwise again, until you are ready to spool the film to the end. You wound the film knob till it stops (this is the initial winding). After a shot has been taken, any further clockwise winding will advance the film unnecessarily. Turning the main knob on the camera will advance the film to the next ready position.
Another reason for your troubles... It could be that when you mount the film-back onto the body, the small windows -- one on the body, and one on the film-back -- are mismatched. When you mount the two, make sure they are either, both red or both white. One red, while the other is white will cause a mis-time with the winding.
Hopefully this makes sense, or at least, helps.