Self-doubt is normal. Everyone goes through it in nursing school
. Anyone who does not scares me.
I cannot give you specific nitty gritty advice on what nursing instructors are looking for because I have given up on that question lol. Their expectations on the little things vary wildly but, all in all, everyone in a position of leadership likes a person who is receptive to guidance. If your professor makes a suggestion, chances are it's not really a suggestion. Follow it. If your professor gets annoyed, say "I will do XYZ next time" and do it. You'll learn first hand all the ways people get to Rome, and which ways you prefer.
The phrase "I don't know but I will find out" has never failed me.
I come to clinical rotations way early in the beginning. With permission, I poke around the unit to see where stuff is. I try to make sense of their organization scheme. I may not know where the 12 french soft tracheal suction catheter kits are but I know this big drawer has respiratory supplies.
If you open a cabinet for one particular item, take a millisecond to scan what else is in that cabinet.
Find out where you can read policies and procedures.
Accept that your professor's annoyance is not really a reflection of you. No one knows everything in six hours, much less a student. It's a personality quirk of hers. Brush it off.