If you understand the concepts and have practiced creating and customising the sample app in a dev org, you should be well prepared.

The exam is not primarily about testing your memory of things like number of X, limit of Y etc. There may be some of those, but mostly it's about testing your knowledge and logic.

And as for sample exams online - many of them are at best out-dated, and at worst can be totally misleading with poorly worded questions and incorrect answers.

So don't be disheartened by online exams not going your way - take comfort in the fact that you understand and have practiced the core concepts. Good luck.