Using carvey to size material

Hi everyone, I’m looking to cut excess material off of a larger piece of wood. Basically, I want to cut a 12"x8" piece of wood into an 11"x7" piece. Easel only let’s me make box cuts, but I simply want to make a nice, clean, straight ‘L’ cut (I’m doing this because I don’t have access to a table saw or something that can keep a true line). Is there a way to accomplish this?

Thanks!