So you've entered the lock and managed to get the stern line onto the bollard and the boat is stopped. You "tighten" a bit too much on the stern and the bow starts to point further and further away from the lock wall.
Ensure the stern warp is secure and turn the wheel into the lock wall and engage forward drive (no serious power). The nose will gently come round enabling the person for'ard to pass warp to lockie or loop a bollard (and you might get a round of applause from onlookers!).