how can i make sure i have autism?

@imaginativeAcres3354  You rightly said that online tests are starting point but not enough to confirm a diagnosis. The only way to get an official diagnosis is through a professional. They will do various assessments, such as behavioral observations, questionnaires, and sometimes even genetic testing. 

But it's important to keep in mind that it's often best to communicate openly and honestly with loved ones, especially if you're experiencing difficulties or have concerns about your well-being. It can be helpful to explain the reasons why you're seeking an evaluation and the potential benefits of receiving a diagnosis, such as better understanding of your own behavior and needs to say the least. I went through same challenge and relate a bit. Take care.

@imaginativeAcres3354

Depending on your country, I know it is possible to request you DON'T have input from your parents when being assessed. It can make things a little more challenging, but it is possible.

The only way for an official diagnosis is via an assessment by a professional. 

However, it is often very beneficial for those in our lives such as parents to have awareness of our needs and struggles so that they can understand how to help us best. 

Why do you need to make sure you're autistic?

What would that functionally do in your life?

Are there supports you need? Accommodations? You can pursue those without a diagnosis in some cases, but you'll need input from a professional for more intensive care.

For any major changes (starting therapy, changing school accommodations, etc) you'll need your parents input. I had unsupportive parents growing up and I know how difficult it can be. Still, it's the only way forward until you're an adult. (I'm assuming you are a child.)

Talk to your parents. If that doesn't help, talk to a trusted adult at school or elsewhere in your family. Let them know you are struggling and that you need help. That is my advice.