Hi tzeremakos,
The sections of questions in the
OG are arranged in 'general order of difficulty', meaning that a random question near the end of the PS section will likely be more difficult than a random question from the beginning of the PS section. However, that does NOT mean that every question is more difficult than the one immediately before it.
Many Test Takers spend too much time worrying about the 'implied level' of the practice questions that they're working on, when they should actually be working on other things (Tactics, pattern-matching skills, developing proper Test Taking habits, etc.). At this point in your studies, are you getting more questions wrong because of silly/little mistakes or because you find the questions to be too difficult?
GMAT assassins aren't born, they're made,
Rich