You need a strong clamp to connect your 10 gauge to the rail. You were given good data.
That stuff is junk, it is not soldering, and is NOT for electricity, it is GLUE for copper pipes!!!
From the site:
Will not conduct electricity , Tensile strength in excess of 1000 psi
You were given great suggestions to make track power work, and you did not follow any of them except get large gauge wire.
You need to clamp, mechanically join the wire to the rail, where everything is clean, or has an electrical antioxidation compound.
I can guess you used nothing in the rest of the rail joints.
Sigh....