I made it through chapter 8 of Fixnum, but I started to lose interest in chapter 9. Chapter 8 got me to macros, which seems to have completed the bulk of the language. Chapter 9 shows how to do structures, which aren't really part of the language, but are added with macros. The same thing is done in chapter 10 for tables and chapter 12 for objects.
By chapter 12, I'm just skimming through so I get completely lost in chapter 13, which is about call-with-current-continuation, also known as call/cc. I really don't get what it does, except that it has to do with jumps. Not understanding call/cc ruined me for much of the rest of Fixnum. While the fast pace of the first half of Fixnum was good for me, the second half moved too fast and lost me.
That's ok, though. I learned enough to be intrigued with Scheme; I will look to some other resources to continue my learning. Later I can come back to Fixnum and will hopefully do better.
I've ordered The Little Schemer, which has received great reviews. My understanding is that it starts out very basic, but gets pretty difficult at the end. It has been praised as one of the best written computer science teaching books, so I'm looking forward to it.