Except we LEASED it. And we let the lease expire (which admittedly we shouldn’t have, but we did).
Also we DIDN’T expand it in the 2010s. So the “we dug it” argument got seriously post dated.
The wording of the Hay–Bunau-Varilla Treaty stated that “the Republic of Panama grants to the United States in perpetuity, the use, occupation and control of a zone of land and land under water for the construction, maintenance, operation, sanitation and protection of said Canal.”