Barrel droop refers to the (unfortunately) common habit of spring rifles, most especially break barrels, to have a barrel that does not run in the same horizontal plane as the air chamber of the gun. What this means is that the scope, which is usually mounted on top of the air chamber, has a horizontal line of sight based upon the horizontal plane running through the center of the air chamber. You can change the scope's line of sight of course, but generally the scope's line of sight will mirror the air chamber's line when the scope is in a neutral set-up. Now, picture the barrel of your spring rifle extending out from in front of the air chamber. That barrel only needs to be oriented a fraction of a degree downwards to dramatically affect the flight of the pellet by launching it along a horizontal plane that is angled slightly downward from the plane in which the scope points. Often the droop is not noticeable to the naked eye but becomes readily apparent as soon as you shoot the gun. If not recognized, droop can cause the shooter to start cranking up the elevation on the scope to overcome the downward angle of the barrel. Note, this is not a condition that results from the barrel not seating properly after being cocked, but is the result of slight imperfections in the manufacturing process that result in a barrel/air chamber pairing that is not "true". The best way to resolve this issue is with droop-compensating mounts or rail bases that have a very slight cant, or downward angle, built in. With compensating mounts or bases, the scope can be set up and zeroed without having to crank the reticule to the extreme upper limit of the scope's mechanism. Another approach is to "shim" the scope, meaning to place a very thin piece of material directly on the rear scope mount, just underneath the scope itself, and introduce a downward angle on the scope that way. Shimming works but you must be careful not to add too much material below the scope or you will like damage the scope's structure when you tighten down the mount tops. YouTube has a large number of quality videos discussing both air gun droop and scope shimming - well worth a look.
By the way, three of my current six spring rifles are Nitro Piston rifles from Crosman/Benjamin. All three have some degree of droop and I've used both shimming and compensating bases to correct the problem. I still love the Nitro Piston system; I find it smooth to operate and powerful for the class of gun. That said, if locking down those screws doesn't seem to make a difference (and be sure to lock down all the screws, including and especially the mount screws for the scope) then definitely take up Benjamin's offer to replace the rifle. Life's too short to waste time sussing out a problem like this unless you happen to enjoy that kind of mechanical sleuthing. My 2 cents.