you hold C to look behind in car and turn the camera back to trick the game into looking 360 around and then you follow specific path. (you can look for the path in any top speedrun)

maybe try to contact one of the mods here... they have links to their dc so just tell them what happened and if its true there should be no problem getting back (i hope)

ye use rivatuner

what worked for me was that when it asked for the GTA.exe i just launched rockstargames launcher and it somehow worked. Maybe you can try that

I think you should record every run even you don't plan to submit them. Based on them you can improve a lot. Watching your runs back and learning from them is really helpful.

Try going to settings > graphics > and change DirectX version. it has to be 10.1 or 11 (11 ideal)