I think it is poorly drawn. Try semicircles at each end, five straights across the top, one curve in each direction coming up from each side at the bottom., with one straight in between to join it all up.
The proportions of your plan look out compared to the one the NMRA has on their website. It looks like you have too many curves in the reverse curve portion at the bottom of the page. The center of the “C” comes too close to the straight section at the top. That would bring the sections back together at the top. If you read the text, the article is more of a tutorial on basic wiring.
Either way you look at it, the article calls for more 18 inch radius pieces than needed.
See what happens if you use 22" radius curves in place of the 18". Your layout will push out more towards the edges but it will both look and operate more realistically.
You could also substitute in a couple of turnouts and have a passing track on the inside of the 22" radius curves using the 18" radius curves. (Or, slightly larger - say 19-1/2" - if you use flex track.) Except for a short 3-piece section of 18" radius curve, I’m using 22" radius sectional track on the mainline on my 4 x 8 and glad I did.
I don’t have problems with derailing and I can run my trains at top speed* without fear of them “flying off” the layout. (*Mailman, I’ve only tested this a couple of times. So, this is NOT how I operate my layout normally.)