Want To Cancel Prompt, Select No And Still Closes Form

Hi All,

I have a pop up form that requires me to fill out all 4 fields of the form. When I don't, I get a prompt telling me which field(s) I've forgotton to fill in and allows me the option to Cancel (Yes or No) and if i decide yes it wont save and will close the form. BUT when I say No (Don't cancel), it still closes out the form and I obviously don't want that. I don't know if it might have to do with my macro button either? Any clue?

Thanks in Advance!

MY CODE:

Private Sub Form_BeforeUpdate(Cancel As Integer)
Dim blnError As Boolean
Dim strError As String

strError = "You are missing data for "

If IsNull(Me.[Account Number]) Or Me.[Account Number] = "" Then
blnError = True
strError = strError & "Account Number,"
End If

If IsNull(Me.Contact) Or Me.Contact = "" Then
blnError = True
strError = strError & " Contact,"
End If

If IsNull(Me.Department) Or Me.Department = "" Then
blnError = True
strError = strError & " Department,"
End If

If IsNull(Me.Address) Or Me.Address = "" Then
blnError = True
strError = strError & " Address,"
End If

If blnError Then
strError = Left(strError, Len(strError) - 1)
If MsgBox(strError & vbCrLf & "Are you sure you want to cancel." & vbCrLf & "If you do, the info will not be added.", vbQuestion + vbYesNo, "Close Confirmation") = vbNo Then
Cancel = True
End If
End If
End Sub