At your current speed, the lance should couch almost immediately. Aim yourself towards the very center of the enemy horde and angle the lance slightly downward (you're on a horse, remember?) Just keep firing while charging (top speed) until you've cut the distance to the main enemy group to about 30-40% left (this part takes some experimentation and practice).
You should start out wielding a bow, so firing (even if you're flanking, you should really only be going *around* so that you are now charging straight at the enemy body from the side) into the throngs of enemies shouldnt be too difficult. If facing mainly melee archers, veer off early from the main group and start flanking the enemy main body.
