How do I stop missing defects I'm supposed to catch?

You are missing the defects you are supposed to catch, and that weighs on you because you know what is at stake. First, take a breath: noticing the problem clearly is the start of fixing it. Many people who miss things never realize it. You do, and that honesty is what will make you better at this. Missing defects is usually not about trying harder. It is about method. When you inspect the same way every time, in the same order, with your full attention on one thing at a time, far less slips through. Rushing, distraction, and a wandering pattern are what let defects pass, not a lack of care. A steady, repeatable routine catches more than effort alone ever will. Build yourself a simple checklist for what to look at and in what order, and follow it every single time, even when you feel sure. It slows you slightly and catches what your eyes would skip. The goal is not to become perfect. It is to build a process that does not depend on you being perfect.