Access tables are not spreadsheets, and they do not have cells - don't
be fooled by what you see in datasheet view. Access tables contain
records made up of fields.
Each field has a set of properties. The two properties pertaining to
your problem are Data Type and Field Size; apparently your field is type
Text (correctly), and its Field Size is set to two less than you need.
Open the table in design view, set the field size property to a bigger
number and your problem will be solved.

HTH,
Nikos