What do I need to get back to my parent's health insurance?

I need health insurance to help pay for chest x-ray I need to get in school but I cannot register till I pass the requirements which includes the chest x-ray. Once I register, I can go back to my mom's insurance. I was wondering if there is something I can prove that I will be a full time student in the fall and get the insurance so I can use it for the chest x-ray. ;(
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You can pay for the chest xray and then you'll be able to register and get back on the insurance.
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