I don't know to what extent the lowering of compression ratio, due to the use of composite gaskets, would have as I've only ever checked the values on an engine with tin items, but your readings are very low & you are right to be concerned. Even on a 3.5L I've had an average of 155.
I believe when reassembling with just 10 bolts it's advised to install the 'unused' bolts as well & just nip them up. but I doubt that would be a contributory factor to your problem (?)
I'm sure qualified members will be along with advice shortly, good luck !