As above the minimum torque limit is for a good reason. The nut may not unscrew because of the gas tube, but it won't be tight enough to prevent the barrel from vibrating incorrectly and ruining accuracy.
There's a very specific technique of properly installing an AR barrel and if you want good results, you need to follow it.
First, coat the threads with an anti-seize compound. Some people use grease, but an actual anti-seize is better.
Choose one that DOES NOT CONTAIN GRAPHITE. Graphite damages aluminum.
Screw the nut on and torque it down to at least the minimum.
BACK IT OFF and re-tighten again, back it off and tighten to the minimum a third time.
This tightening and loosening process mates the threads on the nut and receiver, and prevents odd vibrations.
Once the nut is tight the last time, check for where the clearance is for the gas tube.
Unless the nut is way off, just tighten the nut until the gas tube will pass through.
If the nut is way off, just loosen and tighten the nut repeatedly until it gets close enough to allow torquing it until the tube will pass.
Like tightening a bolt tightly, every time you tighten the nut, it will screw on just a little farther from the stressing of the threads.
Usually you don't have to do this and you can just tighten the nut until the tube clears.
All this prevents the barrel from loosening and allowing the loose barrel to destroy accuracy.
A slightly loose barrel never shoots good, and unless you have at least the minimum torque on the nut, the barrel will loosen sooner or later.
If necessary, check with one of the Rental Land type rental places to see if you can rent a torque wrench and a large bench vise.
Note that an AR receiver vise IS NOT a bench vise. It's a special holder to hold the receiver while working on it and it fits into a bench vise.
Possibly you can borrow an AR receiver vise to hold the receiver while you torque the nut.
People on this site may be willing to rent you one.
Like all gunsmithing, you can often get by without having to buy a lot of expensive tools, but there's always at least a few you just cannot do a job without.
In this case a real AR receiver vise and a torque wrench.
Without these you're going to either damage the receiver, or have a rifle that won't shoot well.