The add on'collinear' style antennas you have are likely designed only for 2400 MHz and they are not designed to fold flat against a metallic PCB like you have them. They would work well (on 2.4 GHz) if allowed to point straight down (I'm perhaps mistakenly assuming the AP is mounted to the ceiling from your case there). It might look funny if the ceiling wasn't a fairly high one.
Depending on your budget and your DIY-vs buy attitudes, its hard to say what you should do.
You could go to Mouser Electronics, Digi-Key, etc, and see what they have - some are planar and self-adhesive. They can be bought with u.fl pigtails included.
You can buy aftermarket antennas that fit in almost any shape, but keep in mind what their datasheets say especially about whether they need a ground plane.
Since you have two connectors you might have the best luck with two - both being offset by an angle.
Frankly, if I were you, unless you are having problems, I would stick with the ones supplied in the unit (they are the two loops of flat metal in the right upper and lower corners of the unit) unless they are inadequate to your setup.
They seem likely to be a good compromise given the space constraints. If the signal is getting lost, simply pulling the antenna outward might help, remember it was designed to fit into a fairly small box. Since you already have removed the PCB from the box, have you tried moving them around a bit? (specifically pulling them outward so they stick out a bit more, but not so hard that they get seriously bent and cannot go nicely back into their box if later on your decide to do that.)