Exhaust fluid system Fault

What is your question?

I get a Exhaust Fluid System Fault, The dealer says it needs 5 Gals. of DEF Fluid to reset. I add less than two gallons and it overflows. It will not reset even after three time pushing "ok". The truck is just setting right now because it now says In 12 miles, speed limited to 50 mph. From home to work is 17 miles and to the dealer is 15miles (which has zero available appointments until 3 September) I use my truck for work and I hesitate driving it until I get some answers.