That's a lot of layers, top and bottom. On the bottom it does sound like it might be pretty constrictive. Were the Ibex both dry, ie sleeping layers? If so, you shouldn't have needed most of the extra layers. Maybe the down jacket, although I'd probably drape this over me in the bag, for best insulation value.
I wouldn't trust a BA IAC for those temps, just in case I ended up on snow, so I carry a 1/8 EVA pad to put on top of the BA if there's any chance I may end up on snow. ( I realise you weren't sleeping on the snow)
Okay, there's the problem, how do you fix it.
Eat more. Same thing happened to me last weekend. I was on a callout and realised I'd undercooked my bag for the conditions. I was planning on a low of 8C (45F) and took my optimistic MH Fairview 40. I realised about 5.00pm I was going to be cold. Fortunately the Police were catering, so I went for the second big serve of roast beef and turkey with roast veg and gravy plus a side of cheese vegies. Add in a couple of desserts and three hot chocolates, and I had to peel off my thermals an hour after I crawled into my bivvy. I was steaming in there, but the tarp was iced up, so it was at least 0C or lower. Lots of fat is your friend. Take a Snickers to bed with you if you need to.
Next is position. It's a whole lot colder out in the open than it is under a tree. A leafy, dense tree will give you at least another few degrees in reduced radiant heat.
And then, if you're waking up cold, you need to add in some extra heat to your bag. The fastest way to do this is to do some sit ups, in your bag. You're already miserable, so why not? Otherwise crank up that stove for a warm drink, and a hot water bottle to go between your thighs. You'll get colder doing this, but it's much nicer than doing sit-ups.