The key to knowing you’ve tied the weaver’s knot correctly is to be able to release or undo it.
To undo it, you want to straighten out the thread that makes the “U” in the completed knot. No matter which way you tie it, there is one thread in a U-shape and the other thread winding itself around the first.
Pull on both ends of that “U” thread—in opposite directions—to unbend it and straighten it out.
The squiggly portion can be slipped right off, and even the squiggles relax so you have two fresh threads when you’re through.