Your coach was probably refering to 'shoulder fore', which is essentially a shoulder in with less angle. Shoulder in is performed on 3 tracks, where the horse moves the forehand across slightly, to wrap around your inside leg and work on 3 tracks. The inside fore and outside hind work on their own tracks, while the outside fore and inside hind work on the same track.
Your horse is simply bending his neck to the inside, without any change in shoulder angle.
You will find it easier to ask for shoulder in/fore on a circle, where you already have bend around the inside leg, and all you need to do it move the shoulders over and maintain the bend.