I fully agree with mbars' assesment of the situation, get it right before! the deck goes down. Speaking of which, aren't you rushing the deck? If you pour it next week, without proper settling/ compaction, the 3.5" won't be noticed by anyone trying to get across the cracked and sunken deck I can appreciate that you want the project done NOW, but this is a lifetime investment and getting everything done correctly will save you tons of headaches in the years to come.

Congrats on the new pool!