[Goin 4 Broke]

I just changed out a tank for the first time on our unit - 2013 3900fb - and I struggled to get it reconnected. Seems like the hose is about an inch too short. I was able to lift up the tank and get the connector attached, however as I lowered it down it sure seems like the line is under tension. Anyone with similar problems?mmshould I just em pint the regulator a bit lower? Put a 1x6 under the tank?

Related to this, if I have one tank out for getting it filled, do I need to shut off the tank on the opposite side or can the furnace run with a tank missing?