You don't need to create a new datafile; you can extend your existing tablespace data files.
Execute the following to determine the filename for the existing tablespace:
SELECT * FROM DBA_DATA_FILES;
Then extend the size of the datafile as follows (replace the filename with the one from the previous query):
ALTER DATABASE DATAFILE 'D:\ORACLEXE\ORADATA\XE\SYSTEM.DBF' RESIZE 2048M;