The northabout route past Scapa Flow is perfectly viable to reach the Western Approaches, and the only one I use. Cruise at 6 knots to maximize range and endurance. The Channel is not for submarines
But I suspect you know this.
The 'date' issue in your logbook is common, and it happens I think when you save and reload, so you probably played up to the sinking of the Old Raked Bow Split Merchant in one sitting, and then the rest in another?
As for the reversed AoB shots that you took, we've all done it, I sure have. What I try to do is always make my final check a gyro check, because after some experience you can usually instantly recognize an error by seeing an unexpected gyro angle. Even so, scheisse happens.
How are you finding target speed? Surely the estimate 'by bow wave' was a one off due to time restrictions?
Congrats on your successful patrol and good luck on the next.