shift click on form button

Hey there,
I have a little experience with VBA and thus i need help, tx in advance if anyone can share some clues

what i have is a form with buttons, clicking on them changes values in some form fields.
i need the button when shift-clicked to change the value differently

in my code i have

Private Declare Function GetAsyncKeyState Lib _
    "user32" (ByVal vKey As Long) As Integer

and then

Private Sub Bilet1_plus_Click()
    If Bilet1_count.Value = "" Then
        Bilet1_count.Value = 0
    End If
    If GetAsyncKeyState(&H10) Then
        Bilet1_count.Value = Bilet1_count.Value * 10
         Else: Bilet1_count.Value = Bilet1_count.Value + 1
    End If
End Sub

and this works fine when shift-click is used, but it also behaves the same when the next click on the same button comes, even if it is not a shift click.

any ideas how to make it work only the first time?