I think you may run in to trouble with this antenna. At 11 meters or at least US of A CB frequencies, a quarter wave antenna should be about 108" long. This specs for this antenna state that it is only 91.5cm or about 36" long. I see no mention of loading coils to physically shorten the antenna and the requirement to have a specific length of cable suggests that the feed cable is acting as part of the antenna. This could create a bit of havoc in your apartment in the form of interference with TVs radios and such. In the US, the 4 watt maximum wouldn't pose much of a health risk but less exposure is always better. (Think cumulative exposure)
Also, the antenna's proximity to the building may still be a problem especially if there are any metal building components such as metal studs or lathe.
You might trying doing an internet search of coaxial dipoles or magnetic loop antennas. They can be a bit more involved (especially the magnetic loop) but at low power, you'll have some greater design latitude.