OK, at last I'm here to listen to the chapter.
You have trouble with the format of your .mp3 export - the file should be 128 k bits/second constant bit rate (CBR) but what I see is variable bit rate (VBR). I went back and looked at your posts on the 1-minute test and in one you say you gave up on Garage Band and are now using Audacity. One nice thing about Audacity is once you get the settings right the software will use those settings on other projects until you change them.
The rest of your technical matters are fine: opening silence is about 6/10ths second, closing silence is around 7 seconds, mono, overall volume is 87.3 dB (easily in the 86 to 92 dB range).
At ~1:15 the "I" in "I don't want any goat to butt me" gets into clipping - if you listen to it carefully you'll hear that one word sounds distorted. Audacity will show parts of a recording that are loud enough to clip - it's a toggle "Show Clipping (on/off)" in the "View" menu. Fortunately there is just the one clipped spot in your chapter.
So - if you export your chapter again, this time with the encoding set to 128 kbps CBR, and upload it once more, everything should be fine. (Post another message in the forum so I'll know when to check the chapter again.)