Your groups are a lot better than mine where when I first started shooting. Sure, there's lots of room for improvement, but you're starting out reasonably well. So, don't get discouraged.
I disagree with those who contend that putting the trigger behind the first crease of your trigger finger will cause you to pull the gun off line. Those of us who shoot double action revolvers generally will tell you that putting the trigger behind the crease is the BEST way to get a straight pull on a heavy trigger and to avoid pulling the gun off line. Pad on trigger simply doesn't work very well on most double action triggers.
I tend to keep the trigger behind the crease, regardless whether I shoot double action revolvers (which I do about 90% of the time) or single action semiautos, such as my 1911 or my wife's Smith & Wesson model 41. I'm simply more comfortable shooting that way and I consider myself to be a competent shot if not a bullseye quality shooter.
My advice is: find what's comfortable for you and stick with it. If resting the trigger on the pad works for you then, fine, go for it. If, on the other hand, you find greater comfort putting your finger slightly deeper into the trigger guard, then by all means do it.
What I also recommend is two things that others have touched on. (1) get a .22 and practice, practice, practice; and (2) dryfire as much as possible.
Since you're firing a Glock I'd recommend getting a .22 semiauto and not a revolver. There are several good moderately priced ones out there. Ruger makes a number of models that would probably serve you quite well and Smith & Wesson also make an inexpensive model in semiauto.
As for dry firing, do it with a purpose. The most important thing about dry firing is that it enables you to determine whether you're controlling your trigger adequately and avoiding movement as you shoot. Keep your eye on the front sight. Does it dip or bob when you pull the trigger? If so, keep focusing on keeping it as still as you can. A good technique is to dry fire in front of a mirror. If you do that, just focus on the front of the gun and watch to see whether it moves. Another trick. Balance a coin on the gun. Does it fall off as you dry fire it? Work on shooting so that the coin remains flat on top of the gun's barrel.
Several have advised you to take your time as you shoot. No advice could be better than that! Even a relatively light gun can put a fair amount of stress on your arms, hands, and shoulders, if held at arms length for more than a few seconds. Hand shake will result from fatigue and once your hands start to tremble your accuracy will deteriorate. Concentrate on shooting 3 or 5-shot groups rather than entire magazines at one time. You may even want to rest your gun between each shot at first, lowering it for a few seconds to remove the stress from your arms and shoulders.
A final point. Remember to breathe!!! When I shoot I find myself instinctively holding my breath in order to reduce movement. That's a bad habit to get into because, after a few shots, the loss of oxygen to your muscles will increase trembling. So, take a deep breath between each shot.
