Yay it's mspaint drill time again!
I'd get off the beam entirely if I were you. Go back to doing cartwheels and landing with your feet on the line. Have someone watch you if possible to make sure your hips are square, arms come up with your chest/head, and that your feet aren't turned out or doing anything extreme after your done.
After you make 5-10 of those with no problem I'd do them with an 8 inch mat on the floor. Draw a line on the top of the mat with some chalk that's about beam width. If there's a line on the floor you can use, line it up with that one. If not, draw the line out on to the floor with chalk. Looks like this:
Pink x's = feet
Brown x's = hands
The mat being elevated forces you to kick hard over your head to get over, you can't fan and make this. It also compels you to push through the shoulders to stand up in your lunge at the end. Lots of gymnasts muscle their way up because they have great balance...because they can! Can't do that here, the difference in height makes it near impossible and at the very least not worth the effort to try. Easier to push through the shoulders, and since we all like easy the push will happen. One other thing, some gymnasts like to bring one hand up first and try to push through on one shoulder; can't do that here! One handed attempts stop after the first try after figuring out it makes them fall forward lol.
After you can make them (they aren't hard, but they really do force you to kick over and push you'll be surprised lol!) start paying attention to if your feet are finishing on the line. If they are not, check your hand and foot placement in the beginning of the cartwheel. The culprit is usually hands not being placed on the line.
If they are but you can't stick it, then figuring out why is a process of elimination. Either your arms are not coming up with your head, or your hips are not square. Usually this is from the push through the shoulders being focused on, and in some cases overdone, just to make it to the top. Bringing the arms up with the head gets the push through the shoulders under control. Just asking the gymnast to bring her arms up at the right time will typically square the hips also. Easier prevails again! If they are coming up with the gymnast, they are usually even and not dragging the hips out of alignment.
After you can stick 5 of these I'd move to the beam and try some there. I'm a stickler for arms coming up. If I see one on the beam that finishes with arms down I send them back to the mat for 2 before they do another on the beam again.