Don't be nervous. Know this - YOU WILL DEFINITELY get through this OA. By the end of the course (like me) you will be surprised what new things you've learned. You can post questions here on allnurses or look on the web for help. the notes and focused passbook TheCommuter mentions might work well for you. Don't waste more time than you need. If what your doing isn't helping you improve on the ATI pretests, change it up. Looks like you can post here, maybe TheCommuter can make sure you have the best notes. I can't remember why, but I very much wished I had posted here, like you, when I was struggling. Would have saved a lot of grief, too, and wasted time.
I took C228 six months ago. Passed the OA w/ a 74%. I think I had to take that ATI pretests over and over again, maybe like 8 times before I was scoring high enough to take the final OA. I just skimmed the readings in the COS. I was new to community health nursing. I was fortunate to work with a WGU BSN grad. She had even worked as a Community nurse for the Red Cross in Oakland, Calif . (I have ZERO community health nursing experience). I had no idea what a parish nurse was, and a lot of the other stuff, but was able to learn a great deal from my new friend - she had actually worked with parish nurses.
Best of luck. You'll get through it. You're not alone.