I stumbled on this sentence, because I don't know how to translate "nara".
Usually, "nara" means "if", but in this sentence, if you translate it as "if" it will be weird, because the part following nara is in the past tense and has the particle ので at the end.
Besides, this sentence has three particles: と, なら and ので and when you put them together in one single sentence it makes it more complicated.
This is my translation to this sentence:
After confirming reservation, if next weekend, because we both had spare time, we gone to book spa hastily.
You see, the translation doesn't make sense, so there must be a particle I misunderstand.