Help pls! I have no idea when to cut it, it's my first time

Pretty much done. Personally I'd either chop it this weekend or next weekend.

wait a week

It's safe to trust the trichomes at this point... Based on what it looks like, you seem to be at the end. So it's just a matter of scoping trichomes and guesstimating some overall %-amber and going from there. how much amber? 10%? 70%? The higher you go the more couchlock/sleepy the effect is. However, just as Nyqul puts some into a coma and others it makes hyper, you may feel differently about it, even if low chance that's true. Good to experiement with early-to-late harvest windows to find what you prefer best. also, you should assess more than just top colas (never leaves). Scope the mid plant buds and lower buds. consider a staggered harvest -- don't expect a better yield, but more consistency of ripeness, so it may or may not be cost-effective to do it. Even so, i'd suggest taking off at least a nug or two at various points - label them with %-amber or otherwise distinguish early-to-late ripeness. Find out what you like after you smoke/eat/vape it. Shoot for that target in future. Take the bulk off when you think it will be best, but don't ba afriad to take a nug off early or maybe leave a couple nugs to ripen longer. Take note of any shrinkage differences -- it will shrink quite a bit as it dries. If it shrinks signifcantly more than the more ripe nugs, you know that's too early in the future.