Drive through the legs.
Instinctively you may be pulling on the handle, which will reduce the amount of power from your legs.
To combat this:
Straighten your arms and make sure your elbows are locked.
Concentrate on the legs by pushing off the footplates.
Pull the handle into the lower ribs at the end of the movement.
The legs are much stronger than your arms, so use them. You will have a larger power output by using the legs and your row will become more efficient.