Feng, I know this may be hard to hear, and I don't know your parents, etc. However...I think you need to let them know about the situation. I unfortunately do not see any way of you being able to ship the betta without a) doing so through a little fish shop or trans-shipper who can handle the mailing or b) meeting up with a stranger.
I know we have a wonderful community here, Feng, but as a parent with a teenager, and as someone who grew up online, I can tell you that I would never, under any circumstances, want either of my children meeting up with someone they only knew from the internet, no matter how wonderful and well mannered and sweet that stranger seemed online. And as a mom, I worry about you, too, even if I don't know you. You seem a sweet and wonderful person, and I want you to keep safe practices.
I would hope--though of course I can't know--that if you told your parents this whole story, they would understand and help you find a way to ship the betta safely.