MS SQL Management Studio - Script of INSERT statements leaves empty chars for shorter than limit NVARCHAR?
I believe that the underlying data in your table has additional spaces at the end.  You can verify the actual data length with a query like:

SELECT LEN(StudentName) FROM dbo.Students WHERE StudentID = 1


If it's not 4, then it's storing more than just 'Mike' and SSMS is simply preserving your data.

If you don't want the extra spaces, you can remove it from your data thusly:

UPDATE dbo.Students
SET 
    StudentName = LTRIM(RTRIM(StudentName)), -- older db compatibility levels
    StudentSurname = TRIM([StudentSurname]) -- new db compatibility levels