Specifically, Romans 3:21-26.
Aye, of course it's logically possible God simply won't forgive you. But the basic fact is that logic doesn't hold much with God, and we all know He will.
Here and now, what you did in the past is not so much a threat to your salvation as your doubt is.
You see, nothing man does or has ever done can ever be enough. The works of man are useless to earn our own salvation.
That passage you read speaks of a new justification; not of law, of works, but that of grace, through faith. You can read further through Romans 4 on how Abraham, was counted righteous for faith, not works, and how we, likewise, are considered his spiritual children because we face the same deal.
Romans 5 is about how sin simply can't compete with grace. That's why your past deeds are null and void once you enter this new covenant.
Romans 6,7,8... you may as well read them all.
We all know God is sovereign and nobody tells Him what to do. But we all also know that He is trustworthy, the Most Trustworthy of all.
Yet even more importantly, He's your dad.
You see, we've all been adopted.
(note; adoption: huiothesia, -pronounced hew-tea-seah?- means "entering into a new family relationship with all its privileges and responsibilities").
When we're thinking of adoption, we're not talking about hiring employees. We're talking about full-fledged kinship. And this will not include the things you did before adoption. It's a full step, leave all behind, stand before God 'born again' status. Once you're adopted, nothing in the past counts.
Trust Him on this. Your Dad has a place for you at home.