The "cardboard thing" is just there to keep the bolt in place while in packaging. Discard it as it's not needed. Leave the cap off during installation, then place after everything's together. It's basically a dust cap. It isn't truly needed, but will help with longevity.
I totally mangled my crankshaft and threw one set of bearings from another car I found in a junkyard, add thicker oil because why not and my engine has been running like a champ for n3 months. The machine shop isn’t necessary