How would you translate this sentence? I'm not sure about the meaning of 限り.
限り means "limit". Following a verb it has the sense "within the limits of [whatever the verb means]", "so far as . . ." For example: 僕が知っている限り means "so far as I know". Here, わかる限り means "so far as I understand". The whole would mean "I was surprised, and I heard/listened to what was said so far as I understood it, and so I report it [now]". Note that を marks 話 as object of 聞いた, not of わかる.