help me Rhonda help help me..

I just made a wool cloak in an hour for tomorrow. Let me tell you it's quality. Actually for a 1 hour cloak it's really not bad, two half circles gathered at the neck line sewn to a rectangular hood with radiating cartridge pleats at the top. 

My question is, who's put arm slits in a cloak before? I kind of want to so I can wear my muff on the outside of my cloak. but I'm nervous about putting them in the wrong spot. you only really get one go at it! 

Thoughts? Tips? Don't do its?

Now on to the next project, a quick and dirty 18th century cap...