Atom sizing - leaving for Machu Picchu

Hey guys

Leaving next week and here is how I had planned my layers Base: Icebreaker merino Mid : Patagonia R1 Insulated: Atom Rain layer: Black Diamond Fine line

Got my Atom large today. It feels a little loose over just the base layer. I am 5’11”, 183 lbs , 41” chest and 36” waist. When I tried medium at the store it had felt like it was a bit too snug.

Would love to get any inputs on the size. May have to head back to local REI to try medium and see if I want to swap size. Hopefully they have medium.