If they think you're ready to test, then you are. If your instructors could see you having any difficulty with your kata or basic techs, you wouldn't be testing. My instructor has on more than one occasion delayed a student's test according to our informal testing calendar because he felt the student was still a bit shaky, needed to work more on their forms, etc. It's not at all uncommon.
If you've moved confidently, easily and correctly through your kata at least once, then you know them. That one performance is all the proof you need. They're in there. So your job now is to understand and believe that. If you do, then the performance that's in there, waiting to emerge, will not be sidetracked by mistaken doubts.