Type II idiot here...
Last patrol was sort of like yours..I was sent to the Shetland Islands, which is probably on the extreme end of the range for this boat (IIA). You need to manage your fuel and the best way is to try and set engine revs yourself. In the command room, look at the engine rev counters, then set the speed...ideally they should be around the 3000 RPM mark which will give you a good speed/mpg ratio. Ask your navigator how far you can go with the current speed and then calculate how far your whole trip will be, to make sure.
I also had a similar patrol where nothing was sighted until the very last hour (of the 24) on my patrol sector. That's the life of a Type II man I'm afraid. We get all the scraps and have to contend with limited fuel, basic comfort and hemarrhoids. Face it...we are second line troops...just an after-thought for Hitler. We are the fat slob of a soldier left behind the lines cos we're basically useless. And that's the way we like it. Some people like to play the hero...some like to play the insignificant, useless, slob of a Captain...sort of like a Thomsen in Das Boot. Cigarette hanging from his lips, boiled egg in his pocket, drunk and puke stained coat. Welcome to the world of the Type II.
p.s. Anyone who reaches 100k tons in a type II....time to move to something bigger, matey. Highly unrealistic.