There are many more knowledgeable people who can offer assistance than I, but from your question, my first thought was to wonder if you were having a site issue or a user issue?
After 700 rounds, if your sites are off, you will see most of your groups falling to one area of the target. If your hits are more randomly scattered around the target, then you have a user issue.
Sooo.... one way to determine where your sites are hitting is to support your Glock on a sandbag and seeing if you can keep the weapon steady enough to see if your shots are landing in one area. If you site, using a sandbag, dead-center and you find your groups falling, for example, low-left, then you may have a site issue.
Have others fired the weapon? What were their results?
Remember, the _smallest_ change in your front site picture will have a _huge_ difference in where your shot lands.
Also, calber/recoil will have a huge difference also. For example, when I had my .380 PPKS, I could drive tacks. Same with my 7.65mm PP, my Ruger .22 and the FN 5-7 I played with. All these are very easy caibers to control.
My .44mag I can't hit the side of a barn with. Not the weapon's fault, the Ruger is doing fine. My accuracy increases with light loads in the .44.
I am not a good shot, but I pretty much know the source of my issues, and the sites of my weapons are not proving to be the issue.
Pier23 gives good advice. If it's the sights and not you then the correction if fairly easy. First, do you have fixed sights or adjustable? If adjustable you move the rear sight to the left if your shooting to the right, to the right is your going left. Same with fixed sights. But you will need a mallet and pin punch to move the rear sight. As far as high or low, go to a gunsmith to see about shaving off a bit of the front sight, or getting a bigger sight as the case may be. Before I did any adjustment I would get a a good shooter who uses your make and model and have them try it out. Good luck.
If you have the factory fixed plastic rear sight, and your shots are high or low, Replace it with a different height sight. Having been a Glock dealer for many years, I found it essential to purchase a Glock sight replacing jig and it came with a bunch of rear replacement sights, on the side of the sight there is a line that designates the height, one at the bottom, one at the center, and one near the top.
If your sights are not adjustable, then you need to adjust your point of aim. However, I would see a local gun smith and ask him if your sights are off. SInce you are new to shooting handguns and you have selected a very snappy round to shoot, without watching you shoot, I would lean toward shooter issues (no offense intended). Accurate, consistent handgun shooting is not an easy task without help and guidence. I have been shooting hanguns for 30+ years, shoot competitivley, and I am firearms instructor and I still use an instructor to work with me.
I would be willing to bet it is not the sights but the shooter, no disrespect intended. Fire off a sandbag if you are not sure and as another poster suggested, have an experienced Glock shooter try the gun.
Hey Jake, Peir23 gives some good advise. Another thing you can do is to check out this link. They make targets for this as well that can give you an indication of what may be causing you shots to be off from point of aim