we were all so emboldened by the fact that not only had we d

这里是 not only 放在句首,此时 句子要部分倒装.部分倒装就是疑问语序.
这里正常语序是 we have done it,部分倒装就是 had we done it.
例句：
Not only did you have no time to have breakfast ,but also I missed the early bus this morning.
这里that 引导的结果状语从句.so,that ,如此,以至于,
如果还有疑问请继续追问,