Theory test

So ive had the theory 4 in 1 app for a while now and have studied most of the sections and do really well on the quizzes that they can allow you to do as a practice for that section.

I get 80-100% almost everytime but the second i do the mock test section, i struggle to get over 37 questions correctly and its always for the highway code questions. Is it because im just nervous for the actual theory or am i really that stupid?

I know people say that the theory is just common sense and that is what i do for most questions(i still read them and the answers i can choose) but it also makes me feel slightly embarrassed when i struggle to get even 40 questions right and im still only doing a mock test, if im struggling this badly then i cant even imagine the real thing