Just took my first practice MCAT

Wow, I mean were should I start. Well, it was the princeton review diagnostic 4011 MCAT exam(first exam you take in the class.) Just getting through the passages and not forgetting what I had read in the last paragraph was tough. I mean the passages were at a very high level, verbals were the most difficult to understand, than PS, than BS was the easiest probally. I would expend all my energy and focus just getting through the first 2 passages before I felt exhausted. I had to stop the test on multiple occasions to take a break, cause I would have to put my utmost focus to read a passage for comprehension and answer the questions only to have another 4 passages with equal difficulty waiting for me. I dont know how to take this in and were to go with it. In fact, I haven't even finished the test. I was able to get through about half the BS(final section) and now im spent already.

Do I just have to take more n more to build up the stamina? I think the tough part was that the way the passages were worded and what not made me have to really focus in to comprehend what was being said (especially verbal were I was still lost.) ugh.