How much is an awful lot in cm? inches? Is the sag at full extension only? Is your mount connected via the studs? The extra picture is an anchor for wallboard and I sure wouldn't trust that for mounting in any case.
None of my mounts sag like that unless they are fully extended. Are all the connections tight? Thats where I would start. It doesnt look like its going to fall or anything but is angled slightly from the weight and there is either some slop in some of the connections or the mount isnt designed to hold it horizontally level. Just my $.02. I have 6 tvs on wall mounts and have mounted quite a few others. Some tend to have a little sag but not as much as your pic suggests.
If I tighten everything completely down, then it won't swing or extend... I'm thinking I just need to return it and get a quality mount. Does anyone know if I can reuse the holes in my wall and studs for the new mount (as long as new hardware is same size or bigger), or do I need to drill new ones?