Matching sides right

I now understand how to do the saddle shoulders (I wrote the other day asking about these) but now I have another question. I did the back of the cardigan, did the right side too, but then found a problem. It says to carry on knitting front until it matches length of back at armhole, but the front already passes that point and I have yet to cast off. I can not see where I went wrong, so does anyone have an answer to this?

The fronts and the back should be reasonably close in measurement. Check and see if the body of the front and back up to the armhole match up and then check that the length from the armhole to the shoulder (or to your needles) match. If the difference is above the armholes, check the placement of the decreases at the sleeve edge. If the problem is decreases at the neck edge, you may have to re-knit and allow fewer rows between the decreases for the neck shaping.

Thank you so much Salmonmac! This makes sense and I will check as you said.