topography in excel

[GeoGeo135]

i am trying to create a topographic map in excel and i have entered the data points and when it gives me a map it will only let me space the lines in 5 unit increments, i need it to be in 3 foot increments. you can see the increments in the bottom of the map. i would attach images but it will not let me 

[#2]

@GeoGeo135 

It's better to share sample file. If not her, you may share on OneDrive, Google Drive, whatever and give the link.