If I understand your problem, you want the form to be Maximised when you open it.
Select Form properties, find the OnOpen event and insert this code
DoCmd.Maximise
If you want EVERYTHING to be maximised when you open the database, then there is an even easier way:
Create a new macro
It needs one line only - Maximise
Save the macro with the name Autoexec
Close your database and reopen it.
Every time the database is opened, the Autoexec macro will run and maximise your form(s)