the caps will spread open, turn into discs almost. like, the mushroom will triple in size, and then the veil will start to tear because it'll be stretched like a canvas.
you picked them way early my guy. the caps didn't even start to spread yet. a couple more days and the fruits would've been quite a bit bigger.
the caps will also lighten up as they mature, not darken. that's where the term "gold cap" comes from -- the caps lighten up then turn a golden color once the fruits are dried.
goal is to harvest just about when the veil starts to separate/tear because if you let the veil fully separate, typically the fruit will dump spores (not a huge issue) and cause a mess. it can be pretty cool, though. i'll have to dig into my archives and find a pic of a pink buffalo grow i did where i ended up with a heart shape of spores on a cap.