New to my gun with a few questions

Hi! I'm fairly new to air guns. My first pellet gun was a Daisy Powerline 1000 which I utterly hated. Almost all the screws were recoiled off and threading gone. Then I got a gamo s1k. I shot about 1,500 shots through it, gamo pellets and jsb exacts. The mainspring then broke and I mailed it back for repair. I got the same gun with a new spring. But my main question is how can I shoot this gun better. So far the best group I can get is about 1" at 10 yards with the open sights. I am shooting from a metal table resting the gun on a rolled up towel. I am shooting at a 15-30ish degree downhill angle. I've put about 400 shots threw my new spring. Any guesses on why my groups are so bad, besides the new spring? Could it be my rest, or using open sights. Also, the barrel doesn't seem to lock in to place too tightly. It can move slightly without being unlached and it doesn't take much effort to open it for cocking, as well as replacing it to its normal position.

I am adding a 4-16x50 Leapers scope when it comes in the mail. Also I ordered a pyramid air gel shooting pad which I will also test out.

Also, any suggestions for tuning my rifle? I ordered a barrel shroud from Rich. Since I am new to air guns, I don't have much mechanical knowledge with them. Thanks for your suggestions!