Having said all that above....here is an alternative.
Draw a diagram on graft paper of the top of the bed. Twin is 39"x78" or there about.
If you take 20" off top for pillow then you have 39"x58" area for the design.
If you leave about 6" on either side then you have a circle of 27". Balance the center.
Assuming this then.
Try to find some kind of measuring stick that has holes in it that you can use like a compas.
If not then bore holes in a wooden yardstick at each 1" or even 1/2". Use this to draw your circles.
Make one template for the curved ends.........and you have it redrawn to the size you need. Work on only 1/2 of the design and flip for mirrow image. Draw the verticle stem in the lower center. This will define the size of the other channels. Does this make sense and help? All you need is ruler or straight edge of about 18" to use as a compas.