At the risk of confussing Bojan with a different technique, I suggest you watch this video by Nefelodamon. The AOB measurement technique is different, but it shows how much easier and accurate it becomes when you wait patiently for the bearing to move. (for example the time it takes for the bearing to move the first 10 degrees, do not wait until the bearings change quickly, take the 1st bearing as soon as you can and just wait) And you do not have to hurry yourselve and become nervous, because that makes mistakes.
http://www.subsim.com/radioroom/showthread.php?t=154461
Secondly, it also shows a better direction to move away from the listening location, more parallel to the target course (that way you are less likely to get too close and be detected). Do not go along the 4th (imaginary) bearing line as that will make the crossing with the 'real 4th' bearing line difficult to see.
And move fast! Surface the uboat and set speed to maximum. I measured up the distance you moved away from the listening location. It seemed to be just 1.4 km. In 9 minutes that would be only 5 knots. Did you do that when submerged? On the surface you could have gone 3 times as far in the same time. Also a longer listening time would have helped here alot. This cannot explain why the 4th bearings didn't cross, but would help to measure range and speed accurately.
Perhaps your sub has turned in the time when you were listening to him. Make sure you have 'rudder amidships' and engine off. Even when the uboat has a small speed speed the crew can make the uboat turn to try to steer to the waypoint mark. If that happends all those bearings are meaningless and you need to do it again. Set 'rudder amidship' and be at periscope depth (it is neccesary to hear him anyway) when you listen to him.