Yes, sort of, ds9 took the cogat last year as part of the group of kids who already tested pretty high on other things, to see about getting into the county gifted program.
He said there were a couple sections he liked, but one he got 'really confused' on. I am assuming it was the quantitative section because that is the one which came in around 35% (!)- iirc.
There isn't really any redo other than some additional testing, but maybe this won't happen at all to your ds. (Additional testing can be done on your own, or if the school will take the request, they might have other testing they can do).
The other thing my ds does is get stressed about stuff he thinks might maybe have happened...but often turns out not to have happened! So, I didn't know whether to worry. Having extra questions at the end doesn't sound promising...

Anyway, we had some additional testing done for a variety of reasons and everything worked out well.
I'm a little surprised they had him do 3 sections in 1 day. I think there are only 3 sections (?) Maybe it was 3 sub tests. Ds had verbal on one day, quantitative on another, etc.