I am trying to make contour maps of the aggregate travel cost by metro in 2017 and the market potential by metro in 2017. I have made the maps on ArcMap, but I am not able to keep the contours inside the U.S. boundaries even those I use a U.S. boundaries

[ElizabethBee]

[ChrisDonohue__GISP]

One alternative is to mask the results so as to just show the United States in the final display.  Check out the variety of possible solutions in this recent GeoNet thread:

smothening edges of interpolated map  

Chris Donohue, GISP