First you should sit down and read your owners manual, if you don't have it I am almost certain Marlin has it online. You will learn a lot about what is probably a gun new to you. Lot's of good info in it, one of my favorites is that you do not need to clean your 917v with regular use. It is a surprisingly clean shooting round in this rifle. I can shoot 100 rounds over a period, run a patch through and only the smallest amount of residue. Any patches after come out clean. I like to clean mine every now and again, with 1 small patch with cleaner, one to swab out any residual cleaner. Shoot 2-3 rounds through it and its ready for the next 150 rounds or so.
I'm not going to sit around here trying to figure out if I can put the bolt in wrong with mine but I will tell you how to put the bolt in. With unloaded rifle, the bolt removed, safety off, I align the bolt handle the way it will slide in with the flatter side/base of the bolt facing down in relation to the rifle. Slide bolt into back of receiver, press trigger, and it should allow the whole bolt to slide forward, turn bolt handle down.
As for a gap between the bolt and barrel, you shouldn't be able to see that with the bolt closed but I can't see any way it could be made shorter with improper disassembly though.
Have you shot it yet? To be honest mine was pretty stiff when I brought it home. I polished a lot of the contact surfaces a little bit and it did it wonders in terms of smoothing the action.