I'm going to spoiler some of this, because I used the film situation to explain why this was probably the most accurate depiction of aerial combat/maneuvering I've ever seen on film.
I actually trained on Corsairs which while vastly different from Spitfires, the avionics are fairly the same and literally everything you want to do requires altitude which means gas.That's why the most tense shots inside his cockpit where when he increase his engine speed. He knew what he was doing, which was basically signing up for a suicide run.
When he ran out of gas it looks like he was at an altitude of ~300 ft based on how small the soldiers on the ground looked. That means he did have some mobility. Flaps are altered by gears and pullies, but since he lost the ability to speed up, turning the way he did cost him a significant amount of height.
He was on approach to make a soft landing, see also: crash (like his wingman did in the water) and could have hopped on a boat and escaped, but he used nearly all of his altitude turning to make that one final gun run on the approaching Stuka. This was why he closed his canopy and decided to go for an actual landing. He was too low to bail out without serious injury, and was also too low to turn again. Dipping his wings at that low of an altitue would have resulted in him slicing the ground and it would have likely cost him his life.
So he took a gamble and went for the landing in enemy territory, which didn't work out for him, but better to have a shot at survival than a pretty much guaranteed death if he tried to turn at a low altitude.
It's not danger, it's acceptance. He knows he's fucked because he used the last of his altitude and has no choice but to ride it out.
This is awesome explanation. Cool stuff. I saw the levers being pushed the second time around and knew it was signifying something.