If you're that tired, a chargey ski like a 187cm Bonafide, that you've never skied, is not the best choice. A 187 or 180! Soul 7 probably would have been easier and more fun. Thus less tiring.
You can also do more low angle powder. It's more relaxing and the sensations can be invigorating instead of enervating of the steeper stuff. But, you have to be ok with it and not think it's lame. The "No friends on a powder day" attitude while skiing alone likely thinks low angle powder is a waste.
Probably, and this is tough, esp on a powder day, you should have bailed on the first day. Rest, do some off snow stuff, get recharged. Yeah, you only had three days. But, you're the one with the complaint and according to Meatloaf, "Two out of Three Ain't Bad"
This year I had two days in Chamonix. I should have skipped the first, I was beat after 7 straight days skiing and the travel. I couldn't get a guide because I arrived too late. Instead, I went skiing anyway, in the freakin' rain and snow. Wet and cold at the same time of day, just changed with altitude. That's tiring without knowing it. Not a great day, it was ok, really only half skiing, but dealing with rentals and buses was a full day. The next day, I was really too burnt to ski, the guide couldn't reach me, so I bailed. Took a nap and got boot work done. It would've been much better to not ski the first day instead.