This is what MLP characters look like in 3D - https://ru.wikifur.com/w/images/e/e3/MLP_G5_EQD_exclusive_screencap.png The head is round like a ball, the neck is a cylinder, the eyes are also round (but partially covered with eyelids and cheeks). And that’s how you should also draw this in 2D. I don’t know what reference you used to draw this, but if you can’t understand the shape from a 2D reference, I suggest you use 3D references from the G5 cartoon, MLP toys etc.
Different styles are mostly about what your lineart and shading look like. But even in 2D a head is still round, a neck is still a cylinder etc. They’re not flat or shapeless. Your reference isn’t the best to show those shapes. This probably caused those problems with your drawing in the first place.
Your reference isn’t the best to show those shapes. This probably caused those problems with your drawing in the first place.