The key here is "REFUNDABLE" ticket - any other ticket and the airline
can play hardball with you deny the refund or just give you a voucher
less the $100 change fee - was it worth it ?
Go with the lamest (no make that least expensive) excuse you can to get pass TSA.

Possible TSA entry excuses (ah er reasons):
Unaccompanied minor
Handicap passenger
Elderly relative (making connection?)
Sky Club meeting
Other airport sanctioned meeting

??? Return to gate area/flight to retrieve article left on board check with Baggage Service for resolution.

Eons (many posts years gone by) reference the UA Club it is on the "E"
Concourse about half the way down concourse and is not the best alternative
for Delta flights (none of which are on the "E")

It would be better if Delta had smaller clubs in more strategic ends of the
concourses instead of inside the main terminal and at mid "C".
Similar to the distribution at ATL one on each concourse.

BACK ON TOPIC ---

Gate Passes may be limited or capacity controlled during Holiday times to
keep security systems controlled. But it is at times like that that the need for
a pass is important enough to ask for it. Unless you have to go to a central
point to get the pass don't take the first NO for an answer go ask someone
else perhaps a 'RedCoat' ! Play nice with the sympathy card and GOOD LUCK !