Probably. You changed Flottila's, but not the uboat type. I think destinations are chosen based on the Flottila and time you are in.
Depending on the year (and mod) there may be a (covert) supply ship in Spain where you can fill up the tanks. Best is to really pay attention to your fuel mileage. The Channel might be asking for more trouble than an empty tank. Likely it is going to get punctured by sharp pointy objects.
Going around Scottland might still be possible if you can refuel. I just don't know the distance of the top of my head.
But you don't really have to adhere to that given patrol grid anyway. The game won't punnish you for not doing this. It's up to you if you want to play uber-hardcore on following orders. The game if forcing you into unlikely situations, so no problem if you don't.