If you say you didn't pack your bag or retained possession of it, unless they found evidence, like your fingerprints on it, all they could do to you is ask who did.
You should watch the CBP shows on NatGeo, that's the standard line offered by the perp's found with contraband in their bags, and they all get prosecuted.
That's the whole idea behind a SCIF. They check everything going in and out of it. And everything inside.
WILLFUL INTENT
A. There is evidence that Mr. Biden retained the classified
notebooks, knowing he was not allowed to do so
_________________
The evidence shows convincingly that Mr. Biden knew the notebooks, as a
whole, contained classified information. For eight years, he wrote in his notebooks
about classified information during classified meetings in the White House Situation
Room and elsewhere. He was familiar with the notebooks' contents, which included
obviously classified information.
_______________
There is also evidence that Mr. Biden knew he could not keep classified
handwritten notes unsecured at home after his time as vice president.
________________
When Biden left office, he knew his staff decided to keep his classified
in a SCIF at the National Archives, knew his notebooks contained
the same type of classified information. As he told his ghostwriter during a recorded
interview in October 2016, the same staff who eventually arranged for careful storage
of his classified notecards in an Archives SCIF "didn't even know" he also had
possession of his notebooks, which he simply took home without informing his staff.