Duplicating and rotating can be a hassle, your best bet is to add a solidify modifier. Regarding the large gap, it is likely due to the location not being applied - to do this simply select the object in object mode and press
ctrl - a and then click apply location.
You can enable Backface culling in blender to see what your model REALLY looks like (because it doesn’t show it properly by default), then you can just add a “Solidify” modifier to your model, it will do everything for you.