User Form with Empty row but user may enter data manually

I am very new to VBA and am trying to put together a user form (Learned to make one this week). The worksheet that it is populating I don't want to be overwritten when the user has manually entered something. They are scanning a huge barcode that I break apart to use, to populate other cells as well as Vlookup to get additional items. I enter the data from the userform in the first three columns, which I hide to the user, and an additional six are hidden. The first column the user sees is Column "I" which is where they may enter information that I want the user form to see and skip. The cells in column "I" also contain a formula to return a value from one of the hidden columns. There are time they will need to manually enter, and this is sporadically throughout the day.

This is what I have

'

Make USAGE active
Sheet5.Activate

'Determine emptyRow
emptyRow = WorksheetFunction.CountA(Range("A:A")) + 1

'Transfer information
Cells(emptyRow, 1).Value = SerialTextBox.Value
Cells(emptyRow, 2).Value = GtinTextBox.Value
Cells(emptyRow, 3).Value = VatTextBox.Value

End Sub