Hi Daria,
First of all, failing in the first attempt is no shame; many do, and only a few talk about it.
However, I need to clarify a few things before I can recommend a better strategy.
If I understand correctly, youhave purchased the PMPrepCast, completed the entire course (all videos), and then practiced with the PM Exam Simulator; is that right?
Or what do you mean by " ... I have done the sample test about 30 times ..."?.
Doing the same (sample) test several times will not do the job (I guess I got that wrong, but it sounds to me that way).
You need to ensure that you UNDERSTAND each and any section of the material. And just watching the videos might not be enough.
A good strategy involves reviewing the content through videos (course), utilizing recommended sources by PMI, such as the PMBoK Guide, the Process Guide, and the Agile Practitioner Guide, among others. AND using a good prep book (like Justice already mentioned), doing short validation quizzes (up to 20 Questions) after each section/chapter to verify if you got it or if you need to revisit and repeat.
Once you have completed the entire content, the time for practicing has come. Do as many (DIFFERENT!) questions as you can and validate why you are wrong and slo why you are correct!
And ensure to do at least 2 to 3 COMPLETE Simulations (meaning full-time, fully-fledged) mock exams.
And do that as long as you feel confident, and then give it another try.
Feel free to reach out for any further guidance.
BR,
Markus