I did the following steps:
1) I went into ArcMap, and from the toolbox, selected, Interpolation-IDW
2) I then put my shapefile as the input and selected the field that I want to map
3) I went to environment settings, raster analysis, and tried to mask the area that I want with the U.S. boundaries shapefile since I want it for the U.S. boundaries only.
It keeps it within the U.S. boundaries, but it cuts off parts of the U.S. I am attaching a snapshot. Does anyone know why this is? How do I fix this problem?