Are my boobs too big?
It's not bad. It's actually totally normal! Some girls develop faster or earlier than others, and it's completely normal.
If you're looking to down play your chest, it helps to get a bra that fits correctly (click here for some tips), and clothes that flatter your shape without drawing attention to your boobs.
I've never been in your situation, but my little sister was just like you and it made her super self-conscious. But there is absolutely no reason to be embarrassed by your body -- it's totally normal, just like everyone else's. Love what you’ve got, and know that you will continue to grow into your bod.