Left crank, correct?

If so, and if it's aluminum and uses a single bolt or nut to secure it to the bottom bracket spindle, there's a pretty good chance the bike was ridden while the nut or bolt was loose and that you'll need to replace the crank, which will have deformed where the crank has been wiggling on the spindle.

For more detailed help, you should upload photos to your Gallery here and then add a post in this thread saying that you have done so. Someone will retrieve the photos and add them to the thread.