The position of your breech relative to the receiver is normal. The lock up can feel a bit funny with these polymer, steel insert barrels, just the nature of the beast. As for your rifle being a real droop barrel gun, that would surprise me on a Gamo, they just don't engineer them that way. I had no elevation issues at all on my Big Cat, which is the same rifle, barrel, receiver as yours. My Big Cat is brilliantly accurate.
If you have tried everything else to eliminate any other possibilities and the gun still shoots low, pop the Gamo trigger back in, contact Gamo and send it back for warranty or exchange.
Pic below is of the breech on my Big Cat showing that the positioning of the one on your rifle is normal.