Hi! Let me share something from a parent's perspective.
It is easier to go with the diagnosis route than not. My child would get access to services, to benefits, to easier college admissions/scholarships. Plus I don't have to put up with the school treating me like crap for going against their recommendation.
The only upside to "going against the grain" so to speak is that I've deemed it in my child's best interest to not to go down this route. For instance, I might not see significant evident of distress in my child's life, and I might want my child to develop an identity outside of any label. For example, one of my kids has extreme sensory issues. We aren't diagnosing it, we .... simply don't force him to be uncomfortable and he's fine that way.
Now, particular to your situation. Your parents are saying you "want to be autistic" - which tells me that they are not seeing the distress in your life, or at least not connecting your distress to a possible diagnosis.
To be honest, I would not take my kid for an assessment just because they scored a certain score on an online quiz. I'm not saying that's what you're doing, just trying to get you to see from your parents' perspective.
I would take my kid in for an assessment if they came home crying, if the teachers told me that the kid is making inappropriate facial expressions, if their essays showed black & white thinking, if they had no friends, if they had social anxiety, etc - all signs that they are in distress, and needed genuine help.
I'd suggest reframing your need for an assessment as a need to get support in your struggles, and being open with your parents about your hardships and in what ways your life is being impacted. If you're being bullied, say so. If you're unable to make friends, say so. And so on...