Xlookup multiple criteria and range to last row

[patriciacosta]

ActiveCell.Formula2R1C1 = _
        "=XLOOKUP(RC[-3]&RC[4]&RC[10]&RC[12]&RC[21],'[Payscale payroll.xlsx]Payscale'!R2C[-8]:R689C[-8]&'[Payscale payroll.xlsx]Payscale'!R2C[-6]:R689C[-6]&'[Payscale payroll.xlsx]Payscale'!R2C[-5]:R689C[-5]&'[Payscale payroll.xlsx]Payscale'!R2C[-4]:R689C[-4]&'[Payscale payroll.xlsx]Payscale'!R2C[-3]:R689C[-3],'[Payscale payroll.xlsx]Payscale'!R2C[-2]:R689C[-2])"
    Range("I2").Select
    Selection.Copy
    Range("I3:I147").Select
    ActiveSheet.Paste
    Application.CutCopyMode = False
    Range("I2:I147").Select
    Selection.Copy
    Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
        :=False, Transpose:=False
    Range("I2").Select
    ActiveSheet.Paste
    Application.CutCopyMode = False
End Sub

I'm learning how to use VBA so started using macro recorded. the attached formula works fine, but not always will go to row 689 or I147. I would like the range to go thru the last row, i tried add last row but it didnt work. If someone can help on this . thank you in advance