I think the book I am using has misspelled this word because according to 501 Latin Verbs it should have only one ‘i’. Which spelling is correct?
Both.
“Rediisse” isn’t a participle. It’s an infinitive. The participles are reditus, rediens, rediturus, redeundus.
This inconsistency is also present in some other forms, and also occurs in the verb “eo” itself. For instance, you may see “redisti” rather than “rediisti”, and “isse” rather than “iisse”. The rule, if you wish to follow it, seems to be that “ii” collapses to “i” before “s” and before “e”.
I haven’t done any research in this area, but I suspect the contracted form is the more Classical one, and the uncontracted forms came into vogue later on, when writers wished to regularize the spelling. I know that this is what happened with forms like “consili” for “consilii”; I seem to recall that forms like “consilii” started to be used in the Augustan period, though that doesn’t mean that the “isse” change happened at the same time.