Do not sew across the rope casings on each long side.
Place the hammock on a flat surface such as a clear long table or the floor. Patiently thread the rope through the first hole of one dowel. Then push the rope all the way down the casing and up through the exact opposite dowel hole at the other long end of the hammock. Pull the rope over and leave about 1. 6 meters/62 inches of it out. Then, thread the rest of the rope down through the other dowel hole on the same short side, then through the casing down to the other dowel hole at the beginning end. The two loose ends of the rope (the other end is an unbroken arc) should measure about 1 meter/39 inches each. Adjust if needed.
If the rope you’re using does do this, tie a firm knot instead.
You could also not create the loop. Instead tie large knots at the dowel entry point to prevent the rope from slipping through, then tie the loose ends around a large object such as a tree trunk or hang from hammock hangers attached to porch poles, etc.
Lengthen the measurements if tall people will be using the hammock. Bear in mind that 15cm/6 inches will be lost from making the hammock.
Use an invisible fabric marker or tailor’s chalk.
Fold the cords in half. Mount the folded cords to the ring with a larks head knot. Slip the ring over an upturned milkshake cup or secure to the work surface in some other way. Spread the cords out and straighten them. Number the ends of the cords 1 through 20. Weave the clew knot using all of the cords - see How to weave a clew knot for precise details.
Make sure that the trees are strong and not dead—ideally, they should be as thick as two arms put together.
If you want to be able to use the item again for its original purpose, avoid cutting it.
If you don’t want the fly rope, you can always cut your rope in two, keeping the head and foot sections separate. Use the tarp as a rain fly. If the tarp is twice as long as you are, double it over and hang above the hammock. This will create a fly for keeping off rain or for providing shade.
