I wasn't at the ground. I actually was off on Saturday, so didn't watch the game. I caught up afterwards, I don't like watching their finals or games if I can avoid it.
Reporters like Oliver Kay (there's an Athletic podcast from, I think, Monday, where he speaks about this) were. As was Rory Smith, as was Henry Winter and Jason Burt. All of them reported that the Liverpool end was nowhere close to full as the match approached, and when the first announcement of the match being delayed was made. Apologies, that may have been 20-30 minutes before KO, not 10!
The French authorities claimed on Monday that 2,700 fans with genuine tickets were turned away. So if we want to say, then we can know that at least 2,700 people bunked in, as a safe assumption. But we don't know when they bunked in, and it certainly wasn't all before the game, or it would have kicked off before 9:36 if they had their end full and the situation outside was 'under control' in the sense of other fans being locked out...