My seashell bra is too big!?

i ordered a seashell top to go with my mermaid tail. It came today and it is only plastic. I tried it on and realize it was way too big! the bottom of the shell is halfway down my stomach. I was wondering if i can trim the bottom a bit but mostly put ALOT of padding inside the shell so it wont look HUGE on me ( and makes me look flat-chested ) please help!