unless 是除非,只用于未发生的事,这事明显已经发生了,所以不适合填
What a surprise it is that you've hiked on Mound Tai!I didnt believe I could do it (even) after I got to the top.
感觉上应该还有一个even,句子就比较通
真想不到你登上了泰山!我直到上了山顶也还不敢相信自己能做到呢.