So I'm new at editing and I'm trying to insert gifs but somehow it always ends up with a gap after the gif ends and looks weird, I have no idea how can I change that :/ can anyone help me please?
A few of the frames (that's the layers in GIMP, they play from the bottom of the layer stack upwards) in the image got nothing at the animated locations initially.
I do not know how you intend this animation to run, but I assume the following:
To avoid a gap at the beginning, you should merge the first two frames of each animated area with the background layer - the one with the cutouts. To do that, change their order in the layers dialog to have these animated parts just above the background and merge down
For the remainder, you will probably want to merge the corresponding frames of the upper and lower part into one - again, change their order so that one is above the other in the layers dialog (doesn't matter which one is above - and then merge down.
You can use the Animation Playback filter in GIMP to run the animation and go through it in single steps: