The tricky part of this game’s movement is that when launching, the launch velocity is just added to your velocity from the orbit. This can, admittedly, be a little unintuitive at first, but I suppose it’s more realistic (kind of? This game isn’t super realistic in general, though). Because of that, the marker is not entirely accurate, because it does not take the orbit into account. For best results, you need to launch off the tangent of the orbit (the line perpendicular to your current position on the circle) - that’ll also give you the most speed!
Regardless, I’m happy to hear you had a good time with the game :)