I would like a message to pop up on my spreadsheet if an entry is either blank or greater than 20. Currently an error message will pop up but it will allow the user to navigate to the next cell without correcting the information. If the user inputs "25", I would like the message to pop up and then the original cell to be selected in order for the user to be forced to put a value between 1 and 20.

My current code:

Dim strCurrentCell As String
    Dim strB3 As String
    Dim strB4 As String
    Dim strMessage As String
    strCurrentCell = ActiveCell.Address
    strB3 = "$B$3"
    strB4 = "$B$4"
    
    'Data entry controls

    strMessage = "Check your entry for Customers," _
        & " there can only be up to twenty" _
        & " customers per class period."
        
    If strCurrentCell = strB3 Then
        'Assignment of Values from Work Sheet Variable
        sngCustomers = Range("Customers").Value
        
        If sngCustomers > 20 Or sngCustomers < 0 Then
            MsgBox strMessage, vbOKOnly, "Error"
            Range("Customers").Select
            Exit Sub
        End If
    
    End If