350 miles? Where are you getting that number from?
The CBP has it at approximately 321* miles (
*mileage and material totals are approximate and rounded as construction activities are ongoing)
https://www.cbp.gov/border-security/along-us-borders/border-wall-system
That number was "Last modified: September 14, 2020"
And most of it is replacement for "dilapidated or outdated designs," not a new wall.
One of President Trump’s central 2016 campaign promises was to build a wall at the southern border. That effort is now well underway, with his administration aiming to have completed 450 miles by the end of 2020.
www.foxnews.com
As of late-June, 216 miles of new primary and secondary border wall have been built since January 2017.
Of that, most is in place of what CBP calls dilapidated or outdated designs. An additional 339 miles is under construction, and 183 miles in pre-construction. In construction, 311 thousand tons of steel have been used and 458 thousand cubic yards of concrete have been used.