Somehow hosting New Year's dinner

I'm due at the end of January and feeling huge, tired and cranky. For this reason SO and I had agreed that this New Year it would be best to just have a nice quiet evening home, make a nice meal and watch a movie.

A couple we are very good friends with mentioned they didn't have plans for the evening, so SO suggested we ask them to join us for dinner, which I was fine with as we are comfortable enough with them to not stress about presentation, or if I clonk out on the couch before midnight it wouldn't be awkward.

Yesterday they call SO to ask if they can bring another couple whom I have met only twice (and found rather pompous) with them. He agreed, mainly because they had pretty much already invited them along just assuming it was ok, and he didn't want to be rude to these people. Normally I would take it in stride, although I do find it incredibly rude when people do this, but I am 9 months pregnant and really do not want to organize an actual dinner party and entertain. These friends tend to do things like this, because they don't feel they have to be "formal" with close friends.

Then ten minutes ago my SO called to let me know there will be 7 of us because a mutual friend is also alone for New Year's, so they thought to invite her too. I am fuming! So rude! But I actually like this girl, so I don't feel like I can take back this invitation I never issued.

Am I being to uptight about this? I feel like besides being poor etiquette, which granted some people just don't care about, it is just inconsiderate. They know I've been going out less the past few weeks because I've been feeling heavy and tired.

SO has told everyone they need to chip in and bring something, so I'm not stuck with all the shopping and cooking (as per usual, since we are usually the ones to entertain). I don't have high hopes though, as thus far all pot-luck meals have ended with this couple bringing over packets of chips or frozen appetizers that I have to pop in the oven. Again, something I usually don't get riled up about, but now find incredibly irksome.

Just....Aarrrrrrrgggh!