I think this is it! I added interfacing, moved the pen holder down so that the bottom gets caught in the seam (just makes assembly a tiny bit easier), and narrowed the inner sleeves a bit (again, for assembly reasons).
I also traded out the hair tie/button closure for an easier full-length elastic closure, because it was actually a pain to sew the hair band and because I'm basically lazy and didn't relish the idea of hand-sewing all those buttons! On the top, it's in the "locked" position (elastic pulled over the back), and on the bottom it's "unlocked". It would have been better with black elastic, but I'm not picky with my prototypes. At least I did change out the white thread for brown. :-)
I also added a ribbon at the top, for a page marker. Kinda gratuitous for such a small notebook, but I like the detail.
I love this floral fabric, and I'm so glad to have found a use for it. It's a "mystery" fabric that I got at a church rummage sale. It feels like cotton, but maybe just a little bit crisper and "vintage-y". The funny thing about it is that when I iron it, it smells just slightly spicy, kinda like Opium perfume! And yes, I washed it! This one is definitely a keeper, and it's mine. :-)