No shame in using gamesaves while you're learning. Consider it training time. I did my first couple patrols like that. It's the only way to learn what works and what doesn't. I also recommend learning how to use the mission editor to set up basic attack scenarios. That way you can try many different things without having to spend hours of patrol time in-between.
When you finally bring yourself to the point of not using gamesaves, you get an even more intense nervousness/excitement when you're about to hit that Fire button.
As for you're torpedo problem. Do you have auto-targeting on? If so, you shouldn't have to send any data to the TDC.
Also, firing at something that's at 300 degrees from you is a potshot anyway... the torpedo has to turn approximately 60 degrees depending on the target's speed and direction (aka 60-degree gyro angle) and that will kill a lot of your accuracy. It's better to set yourself up to fire with as small of a gyro angle you can get. Now... that doesn't mean to wait until he's at exactly 0 degrees in your scope, because you have to take into consideration the fact that he's still moving, and the TDC will calculate accordingly, creating a gyro angle to compensate his change in position from the time of firing to the time of torpedo impact. To find your gyro angle, go to your TDC panel and hover your mouse over the lower dial (your ship). This will only work if the TDC already knows his speed and Angle on the Bow. If you're using auto-targeting, the TDC should have that information (I think.)
If you're able to reproduce what happened, take a screenshot right before firing. Make sure it has the periscope view, and all three side panels (TDC, Data Input, and Torpedo Console) visible. This will help us narrow down what's happening.
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