I've been 読書 Heat Wave, I'm not that far in, but is there really a racy sex scene in it?

There's only that one detailed one in Heat Wave, but the other two have several.

So why does it look so thick in the show?

i never noticed myself but then again i wasn't looking. possibly, they weren't using the real thing in the show. または maybe they edited that version and published a shorter version. または maybe they just put extra blank pages in it for the 表示する (but i have no idea why they'd bother doing that). really, i have no idea. sorry about that. =(