I understand the conundrum you are in. My parents and siblings were and are not accepting of my professional diagnosis, as they had years of a "moral diagnosis" of me that they had already set their minds to and were not going to change their minds, even if a professional did the diagnosis.
If you get tested before you're 18, then technically, you fall under the "pediatric" status and can have much of this testing done for free or with a minimal insurance co-pay, but this requires your parents to sign off on the testing. Once you turn 18, you're not under your parents "thumb" anymore, but now testing can be expensive, and at 18 you probably don't have much cash flow.
If you are in a situation where you are likely going to need work accommodations, legal assistance, financial assistance, then you need a professional diagnosis in your medical record. If you are like many other folks, you have done tests like this, and chatting with other autistics, things sort of "fit" with the diagnosis, then you can be considered one of the many who are "self-diagnosed". However, there is also the risk of misdiagnosing yourself.
If, for many reasons, you are self-diagnosing based upon all your research and understanding of the condition, then my best advice is to really look hard at the many aspects of the condition, adapt, and overcome as best you can. Do not expect understanding nor empathy, as most only associate autism as a debilitating pediatric condition, and not something that is present in "functional" adults.
Welcome to our world.