I'm going to answer your question after I ask a few questions, just to make you think about how you do your cartwheels.
1st question....... What's easier to do? A cartwheel done correctly, or a cartwheel done incorrectly?
2nd question....... Do you have a good carthweel on a line that's done at a normal cartwheel speed and rhythm?
3rd question....... Cartwheel attempts on the beam done at a speed and/or rhythm than your floor line cartwheels?
4th question....... Have you figured out, yet, why I'm asking the first three questions?
Well, if you haven't figured it out, then I'll spell it out for you. You probably do your floor line cartwheels at a reasonable speed that allows your body to move comfortably through the skill, but go an itsy bit slower than the floor line speed when you do them on the floor beam, and slower still when you do them on the medium beam. Are you thinking, as you read this, something like "Well duh! I have to go slower because I gotta give myself more tiume to get my first foot to the beam." If not that exact thought, is there a similar strategy that you use when you do them anywhere but the floor line? So here's the deal.....
Many, like most, young gymnasts get tempted to "play it safe" when they move from the line to the floor beam. I get why that happens, and certainly don't blame anyone for it, but isn't a slow cartwheel kinda awkward? I mean really..... if I told 10 girls to do 100 stuck cartwheels on a floor line, I'd see 1000 total cartwheels done at a normal speed with normal rhythm because none of the ten girls want to do 100 the hard way. Like, who would do that?
So think about it as you warm up on the floor line, and ask yourself if the slow one is easier than the regular speed. If the regular speed is easier, and easier is safer, doesn't that mean that the regular speed is safer and will give you the best chance of staying on?