How do I trust my own judgment when I'm unsure of my scope?

Not knowing exactly where your scope ends is uncomfortable, and it makes you hesitate right when action is called for. That hesitation is not cowardice. When you are unsure of the line, holding back is a reasonable instinct. But living in permanent hesitation will hold you back from becoming who you are trying to become, so this is worth working through. The cure for a fuzzy boundary is to make it clearer, not to wait until confidence arrives on its own. Find out, concretely, what you are and are not allowed to decide. Ask a mentor, read the standard, get the edges named. Much of your hesitation is really uncertainty about the rules, and rules can be learned. Once you know the boundary, acting inside it stops feeling like a gamble. Start by writing down the specific decisions you are unsure about, and take that list to someone who knows. Turn the fog into a few clear lines. Inside those lines, practice acting on your own judgment without second-guessing every move. Confidence is not something you find before you act. It is something that grows each time you act well within limits you have taken the trouble to understand.