Hey Smoku,
Whooaaa hold on a second. I think you're spending way too much time on a preview.
Preview should just be table of contents, index, back cover etc. It shouldn't take more than 2 or 3 minutes.
Spend about 15 to 20 minutes on a postview. Pull out trigger words, look for subtitles etc.
No, you don't have to mind map after preview or during the preview, do it after activating.
500 things to memorize in 20 minutes? Well, maybe, but it's very unlikely. And you shouldn't be trying to memorize during your preview phase.
You're trying to remember everything, instead of just letting it happen.
What's the point of memorizing the table of contents?
You say you forget most of the key points during the preview. So? The preview is strictly conscious, and with conscious memory you must forget something in order to remember something else.
Go easier on yourself, you'll work it out fine.
-JackTuff13