Hmm tough one this, they are very strict on the gates at Houx with cars, but not sure about bikes. As has been stated, you are going to find it a tight squeeze to get everything on your pitch.
Just in case you weren't aware, Houx is the only site which pre marks and numbers the camping pitches.
Even if you could get another ticket this late in the day, I would doubt very much if it would be near the one you already have, but at least it may help get all the bikes in.