My thought is that the bed is modern but the curtains have a very traditional design so whatever you do should marry the two. To make the room more cohesive, I would use the curtains and the bed as the inspiration pieces.

Paint the non accent walls white and the accent wall navy. This will incorporate one color from the curtain and one color from the bed.

Skip the stenciling as it competes with the headboard as a PP mentioned and brings in another design element in the room.

Get different bedding that is mostly white with an embroidered edge in another color from the curtain, maybe burgundy or khaki. Like Pottery Barn's Grand Embroidered sheet set.

Then add an accent pillow in an ikat pattern that uses the curtain's color palette like PB's Aurora Lumbar pillow or their Clara ikat pillow. Ikat is a nice transitional pattern that works with both the bed's modern form and the curtain's traditional design.

Just make sure the accent pillow includes some navy to match the accent wall and curtains and some burgundy or khaki (or whatever color you pick for the embroidered sheets).

Voila! You're done without the extra work of stenciling.