Tbh that temp thing is such a classic beginner trap, and honestly it applies to way more than just bookbinding. I've seen the same exact pattern with people trying to fix their own shoes or even baking bread, where they rush the cooling and everything pulls apart. The lavender oil trick is smart though, it probably helped the wax flow more evenly. I think we all have that moment where we blame the materials, but really it's us not respecting the environment around the project. Once you learn to wait for the right conditions, it feels like everything else in life gets a little easier too. Good on you for catching it before the whole market run was ruined.