i was placed bronze two when i went 8/2 in placements why?

this is not fair at all and I really think riot messed up or something because my duo made it silver 1 we had the same placement games and we won 8 games and lost two I should have gotten at least silver from such good placement games and I played well in all my games I won too. if you don't believe me check my account Trollkillerben I won 8 and lost two for placements and I'm bronze two please if anyone knows why this happened like a riot employee or a someone who knows a lot about the ranked system please tell me.