– your bottle is single layered because the lathe won’t join the splines together automatically, glass needs to have thickness to look right
– the beer can not occupy the exact same physical space as the glass, that’s a 3D thing – 2 transparent objects can’t have their faces in the exact same place or there will be artifacts in rendering – the trick usually is to make the beer a bit bigger or a bit smaller than the glass, the transparent objects either have a bit of space between them (which can look wrong too but not always) or the liquid actually intersects the glass which can’t happen unreal life but it usually looks ok if it’s small and it avoids the ‘face in the same place’ problem.
– your scale is crazy big the bottle is 3000+ cm tall that’s not a real problem (though you can get too big) but it’s usually better to make things more of a ‘real world’ size.
here’s a quick test where I joined the two splines, then lathed that, then made it editable, selected polygons on the inside of the bottle to it has the right shape, Split those from the bottle, closed the top (to make it ‘solid’ beer – which gives beer in the exact shape of the bottle, then made the beer slightly larger with a Normal Move which pokes the beer into the glass but the look is ok
3973_bottle2.c4d.zip
That’s the simple way there may be better ways