IANAL, but I do teach self defense, and have experience with DV during my grad coursework.

One of the main principles I teach the ladies in my class is that the force you use to fend off an attacker needs to be proportionate to the attack. So, if one of my students is in a bar and some guy uses a corny pickup line on her, she can't punch him in the face. If she is walking and is attacked from behind, she can and should use all the force necessary to disengage her attacker, and flee. If the attacker is disengaged, you can't keep wailing on the person or give them one final kick for good measure. The law understands that force is necessary when someone is in danger, but also has parameters in place.

You scratching him will likely not weigh in much; if I was being strangled and the person just removed his hands from my neck, I would probably be grabbing on to their arm as well, as a visceral reaction. People react to trauma in different ways, especially in situations like this. A lot of the times, people "freeze" up, or react on instinct.

If he tries to claim he choked you because you scratched him first, he's probably going to get a stern talking to by your lawyer, or a "really?" look from the judge. Likewise, when injuries are compared, a scratch is not going to hold up against well-documented injuries from an incomplete strangulation attack.

Take care of yourself this weekend. Do something nice for yourself, and practice some self care. You've got this, and you are going to do a fantastic job on Monday.