Ethernet Gauge Too Small for Patch Panel
If the cable won't terminate securely in the patch panel, it's either the cable or the patch panel that's out of spec.  

If you're absolutely certain the cable and patch panel are Cat 6, Cat 6 may be made with either 23 gauge or 24 gauge conductors.  A good Cat 6 patch panel will accommodate either.  In fact even Cat 5 or Cat 3 cable will be made with 24 gauge conductors and will terminate securely in a Cat 6 panel, although it won't perform to Cat 6 levels.  Even quad or some thermostat wire would terminate securely since the gauge is in the working range.  

A Cat 5 panel will typically handle Cat 6 made with 24 gauge wire without a problem, but you may ruin the jack punching down 23 gauge conductors.  

There's lots of sub-standard cable out there.   A number of big online sellers were selling Chinese manufactured cable with counterfeit UL stamps etc.  Some was even copper coated aluminum or tin rather than plain copper conductors.  Maybe you got some of that.  There's also lots of low quality Cat 6 terminating hardware out there.  

I'd try reterminating this cable in a surface mount box and jack from a good quality manufacturer - Leviton, Hubbell, Panduit, Siemon, etc. - try a Cat 6 jack first, then a Cat 5 jack.  

If that doesn't work, replace the cable, but I'd test it in your panel before I ran it.