Just because tongue weight is between the magic 10-15%, does not mean that it is enough. Some trailers will tow fine at 10%, but others can need 15% or more to be stable.
Like others have said, you're are ASSUMING that your weight is distributed properly. You know what they say when you ASSUME, right?
Get the Sherline scale. It's not cheap, but it's cheap insurance because this is your home we're talking about here. If you lose it on the road, you're homeless!
Check your tongue weight and increase it. Get the hitch set up properly. You've got until February to work on this.