I have had the same problem in the past. I realized though that each time I import an updated spreadsheet (particularly if it's in excel format) Caspio tries to ask if I wanted to include new fields.
Below is what I did in the past (other more techncial gurus, might have a better suggestion).
1. Since I import from excel primarily, I went and set the print area before importing. This has prevented the extra columns (which in turn, become fields in Caspio) from becoming part of the my table design.
2. In the "Configure Fields" of the imported table, I have unchecked those fields that I did not wish to be included.
This is just my experience with Caspio, I do hope it helps you.