After I read your first post, my first thought was "I bet one of the bundles is white". Then I read on down and saw the picture.
Roy from PA is spot on. First you need to remove the twists you put into the bundles when making the first loop, then you add the same number of twists back in, BUT IN THE OPPOSITE DIRECTION. This is called back-twist or counter-twist. You will take these out when you make the second loop. If you get it right, when you finish the second loop the bundles will be hanging straight with no twist, or very little.
Back to the white material. The thickness of the strands can vary with the color. This is because the color isn't a dye, but rather a coating. Dye would only "stain" the material, not give us the nice solid, bright colors we like. The brighter the color, the thicker the coating. White is the natural color, and has no coating, so it's the thinnest strand.
To fix this, either add a strand of white or drop a strand of red. Won't hurt the integrity of the string at all, and will even out the bundle sizes.
Hard to tell from the pics, but you may not be getting as tight a twist on the white. Straight off the spool white often seems to be a little slicker to me. A good string maker's wax will fix this.
If you need any help, just holler. I have wax, a video on string making, and discounted string material...and advice is always free. I don't claim to know it all, but after 20+ years and thousands and thousands of strings, I've learned a thing or two here and there about making them.
Chad