Is the rail actually tight to the upper receiver? I have the 9" installed on my G&P and it's rock solid with no sag, It almost seems like you've over snugged some of the bolts causing it to bind against the upper and thus point down.
As for the lower rail not fitting past the bolts, it does...
As previously stated, turn the secondary regulator all the way down (anti clockwise - i realise this feels odd) and it'll vent the vast majority of the contained air. To remove the secondary reg while the tank is rather full can be an arse but I found using a bench vice on the sides and turning...