You're playing League, which is a 5v5 game as a standard. You will always have to rely on your team to a certain extent, however, there is plenty of room for you to just faceroll over the enemy team if you play well enough and carry.
Your MMR is determined solely off of winning and losing (as it should be).
The most important thing about starting ranked is to do it when you feel comfortable with your ability to play every role with numerous champions. You need to feel confident that you have good mechanical skills and have a solid understanding of the game and map awareness.