Don't ever treat a Glock gently... she'll not work well for you. Slam that magazine in with your palm of your left hand (if you're right-handed). It'll get easier, but don't be gentle with a Glock, they are designed to be used and abused. You will notice that it will get a bit easier as you put more rounds through.
This advice is equally effective for when you rack the slide. Place your weak side hand over top the slide, grip the slide firmly, push the Glock forward with your strong side as you pull back on the slide with your weak side as if you were to hit yourself in the shoulder. Train like this because it uses gross motor skills rather than fine motor skills. In an adrenaline rush, your fine motor skills will be shot, but your gross motor skills will still function quite well. You will want to have practiced racking the slide like this, and slamming the mag in as I have mentioned. Word of caution, I have large hands and have pinched a bit of skin on my palm between the mag and the mag well giving me a blood blister as I've slammed the mag in. On the G22 (about a half inch longer) this doesn't happen to me.
Great question and hopefully we hear more from you. Welcome to the forum.