NEED MINECRAFT HELP WITH BEDROCK?

me and my friends made a huge stadium made of bedrock, around 200x200 with walls 30 blocks up and a roof,we were going to use this to have tnt fights and experiments. We were suppose to leave a hole in the roof for access but someone covered it up with bedrock and we cant get in. Is there any way we can get in there or break the bed rock with some sort of plug in or mod or something. ive tried looking it up but everything i find is for bukkit servers, My server runs on hamachi and i cant figuere out what i can do, please help..