I have a hard time keeping it straight

有篇英语文章说老师上课讲的太快，内容太多，之后这个学生就说：I have a hard time keeping it straight. 大家能帮忙解释一下，这句话在这个语境里是什么意思么？谢谢啦～

I have a pen ,haven't I ?还是I have a pen ,don't I ?? Now that I'm only working part time,I have a hard time making___meet. I have not a book. I don't have a book. 都对吗？ I didn't have a clean shot.是什么意思? Paul doesn't have to be made( ).He is always a hard-working student. I have a pen, but I don't have ______ ink. A. some B. the C. any D. a I have a dream I have a rabbit I have a question i have a Q!