my mission I really messed it up and now i unforunaly need to get rid of all my hard work I know harsh how do I do this

In Windows Explorer, go to the folder where you saved the mission and delete the mission and properties files. Be careful not to delete the wrong ones.

As an alternative, you can leave the files there just in case you want to go back to them later, but if you change the file extension they wont show up in the game. For example, you could change

mymission.mis
mymission.properties

to

mymission.mis.bak
mymission.properties.bak