if i main a champ for every role and have 2 back ups. will i win more in ranked?

It certainly wouldn't hurt. Being flexible in champion select is always a fantastic start to any game, ranked or not. Even if it does not initially help you at your current rank it will assist once you begin to climb.

i just tried to be flexible in a game and a 3rd pick went top vel koz he didnt get mid like he wanted.

so even though i practise all this time, someone can just troll and we lose?