Very close, but you should somehow represent the fact that the entire area around the close button - anything that isn't a black pixel - is a big "open a pop-up window to the advertiser's site" button.
And even if you manage to hit it you are thrown in a slightly different looking add of the same thing, with a different x button. And guess what? Theres a third one right behind that x
What's really fun is how YouTube has an X to remove the videogames (!?) it has. And tapping on it doesn't do anything other than change the buttons color for a split second.
I have an app on my phone that plays rain noises for sleeping. It occasionally shows ads, like one that popped up yesterday that featured three pruney old women talking about why they were voting for Trump. Not very remarkable except that above the ad was a fixed label that read "JEWS ARE DANGEROUS" and the close button was barely visible in the middle of this. Never been so afraid of missing that button.