FileMaker defaults to using Exponents for display of long numbers. You can change the format used for display by right clicking ( control click ) on the number field in layout mode, and choosing "number format".
You will get the Number Format dialog. Here you can adjust how the number appears. I believe what you will want is "Leave data formatted as entered"
See attached image.
I should also point out that in versions of FileMaker after 10 All formatting optiona have been moved to the inpspector.
Great help. Thanks!