There is a classic “it’s on the internet, it must be true” problem with some designs. It only needs 1 design to be wrong with a few typos and everybody copies the article and then when you try to make one it’s no good. It happened with me.
See 1/2 watt from Cyrn-y-Brain for dimensions that worked for me.
You wont like Litz wire then! In fact working with 300Ohm twin cable requires the three P’s: practice, patience and perseverance. And a decent knife with a sharp blade.