Code to go to end of current data rather than to a specific row

I have a master worksheet that is kept on one drive and i need users to be able to view certain parts of it in a different drive. I don't want to keep updating two worksheets so have written the follwoing code, which works, however the file size is 20mb which i think is quite large and not sure why.

The master data currently stands at 1896 rows which is why i've written the code to go to row 2000, was thinking, at present, the fact that the code will still be looking at rows 1897 to 2000, even though they are blank, may be a waste and if i can amend this it may reduce the file sizxe a bit?

In row 1 on the user sheet i have just put '=master sheet a1', so the code is just copying this formulae down (currently to row 2000), could this be making it large too?

Private Sub Workbook_Open()

Application.ScreenUpdating = False

With Worksheets("Open Codes")

.Unprotect Password:="melon"

.Range("2:2000").Clear

.Range("1:1").AutoFill .Range("1:2000")

.Range("2:2000").Font.Bold = False
.Range("b2:b2000").HorizontalAlignment = xlCenter
.Range("d2:d2000").HorizontalAlignment = xlCenter
.Range("f2:f2000").HorizontalAlignment = xlCenter
.Range("h2:h2000").HorizontalAlignment = xlCenter
.Range("j2:j2000").HorizontalAlignment = xlCenter

.Range("1:1").Select

Selection.AutoFilter

.Range("a1").Select

Selection.AutoFilter Field:=1, Criteria1:="Open"

Columns("A:AW").EntireColumn.AutoFit
Columns("m:aw").Hidden = True

Range("a1").Select

.Protect Password:="melon", AllowFiltering:=True

End With

End Sub