Hey, don't sweat it...NOBODY gets first builds right. Or the second. Or ninth. And so on. My suggestions would be to...
1) Study what's on the site. Not just the modules, but also look at builds done by experienced synthesists.
2) If you haven't got a copy of VCV Rack, get one. It's free, for one thing...and although it's a bit of a processing hog, it gives you a much clearer idea of what you need to build because it is, after all, a Eurorack simulator. It even has a number of "ports" of various Eurorack hardware modules.
3) Build. Tear down. Build. Tear down. Build. And so on. Think of this as pretty much the modular synth builders' version of using a practice room to work out a musical piece...only, the piece is quite physical as opposed to the usual dotz-n-linez. But like time spent in a practice room, you're honing something into a state where its perfect FOR YOU.
Takes time. Hell, I've been working with electronics in music since the late 1970s, and I'm STILL running into totally new ideas on here.