Of course, the machine must be balanced horizontally, everyone knows that. But the problem you describe has nothing to do with the mirrors or the lens, it can only be because either your nozzle head is not at a 90 degree angle to the bed or your bed is very skewed.
As I wrote before, usually it is no special work to fix it, it requires an exact 90 degree impact angl (I do not know if that translation is correct for it, sorry), the appropriate Allen key and a little patience - however, there must be the possibility for a nozzle head adjustment. If this is not the case, you have the option of replacing it with a lightweight holder from Russ Sadler, for example. Here you also need to be sure that it fits the machine, but at Cloudray they have an excellent service (only my personal experience) and can possibly guide you.