ARAM MMR so HIGH

I am a leisure player. I only play League of Legends for fun. The special modes and ARAM are the only game that I play. Since I never played a ranked game, I did not know what level I am. (I am probably somewhere around Silver/Gold player.) But my ARAM MMR is so HIGH!! It is unbelievable that I am playing with all the Platinum and Diamond players. As results, I feel like I am the one makes the team down. :'( Now all I can do is hoping my team has the OP champions.

My conclusion... The MMR system sucks. It does not really match the same level players. And LoL has became no fun. :(

And...is any way to lower MMR?