Yet another roofing question(s)

Looking for tips on how to get/keep the felt flat on the sheathing. On an extreme pitch it's turned into what seems to be an impossible task to keep from having some waves in the finished shingles. Will this settle down any with time? How bad of a problem is it?
Also, we got a good dump of rain last night. The open portion of the roof was tarped enough to prevent any rain from coming through, but some moisture reached the sheathing by blowing up under the tarps. Does this need to dry out real well before I continue? Looks to be clear weather today and tomorrow and most of Monday, but they're predicting a chance of more storms by Monday night.
For those interested (or just bored) here's some pics of the project so far:
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