If you believe in Jesus Christ as the payment for sin, specifically, your own sin. That God sent Him to be that payment, and that He could only have been God's Son (different than we, of course), you have been moved into God's family.
If Bill Gates adopted you as his heir, and you later doubted if he had actually done it, what would make it true? Your ability to believe he did it or the FACT that he legally made the adoption?
The Law says you are Bill Gate's son, not your feelings in that case, right?
So, The Law of God says if you have trusted Christ as above, the legal adoption is complete... CASE CLOSED.