Probably normal. I haven't taken it yet, but I feel that way about many test, and about pretty much all of UWorld. Even when I know something pretty well I often feel like I'm making an educated guess on a question. Often that's because they're asking for an application of knowledge, or asking it in a way a little differently from how I "learned" it. And I know that I have made careless mistakes on almost every test in the past, so I'm always aware that even if I think I really know this question I might be overlooking something, or making a silly swap in my mind. Like a question a few days ago about CREST, asking for the autoantibody, and even though I've looked at that a hundred times and know it's anticentromere I just glanced down at the choices and quickly clicked anti-SSA and moved on. So on real tests I'm not often 100% confident in any answer. It has to be something that I know beyond doubt, committed to long term memory that I'll never forget, and pretty simple so that I know I'm not overlooking a clue in the stem.
And my reasoning abilities are better than my rote memorization, so things like drugs and bugs perpetually have me thinking "well, I think it's this one, but I can't remember for sure." It usually is, and I usually get most of them right, but it leaves me feeling like I guessed on a lot of questions. And then there are the question that I know I knew at one point and can't remember at the moment. I'm sure that happens to everyone. Thankfully, somewhere in my deep brain my "gut" has me select the correct answer more often than not, but when I get home all I can remember is that it was a question on which "I forgot" which equates to "one I'm sure I missed".