Save As-Overwrite existing File

Anyone have recommendations on how to avoid getting an error when a user tries to rename a file the user is initially trying to save? My file name is stored in cell 3,4. The code then takes whatever is in that cell and uses it as the file name to save. This code works fine if the file doesn't exist. If it does exist and the user does not overwrite the existing file and chooses to rename the file something else I then run into a problem. Perhaps there is a better way to do the code to get the same results.

Sub TestGetFolderName()
   Dim FolderName As String
   Dim txtFileName As String
   
   txtFileName = ActiveWorkbook.Sheets("Home").Cells(3, 4)
   
   
   
   
   FolderName = GetFolderName("Select a folder")
   If FolderName = "" Then
       MsgBox "You didn't select a folder."
   Else
      
      ActiveWorkbook.SaveAs Filename:=FolderName & "\" & txtFileName & ".xlsx" _
         , FileFormat:=51
   End If
End Sub

***this is the function

Function GetFolderName(Msg As String) As String
   Dim bInfo As BrowseInfo, Path As String, r As Long
   Dim x As Long, pos As Integer
   bInfo.pidlRoot = 0& ' Root folder = Desktop
   If IsMissing(Msg) Then
       bInfo.lpszTitle = "Select a folder."
       ' the dialog title
   Else
       bInfo.lpszTitle = Msg ' the dialog title
   End If
   bInfo.ulFlags = &H1 ' Type of directory to return
   x = SHBrowseForFolder(bInfo) ' display the dialog
   ' Parse the result
   Path = Space$(512)
   r = SHGetPathFromIDList(ByVal x, ByVal Path)
   If r Then
       pos = InStr(Path, Chr(0))
       GetFolderName = Left(Path, pos - 1)
   Else
       GetFolderName = ""
   End If
End Function

at the top of my module is

Global TypeSelect
Private Type BrowseInfo ' used by the function GetFolderName
    hOwner As Long
    pidlRoot As Long
    pszDisplayName As String
    lpszTitle As String
    ulFlags As Long
    lpfn As Long
    lParam As Long
    iImage As Long
End Type

Private Declare Function SHGetPathFromIDList Lib "shell32.dll" _
    Alias "SHGetPathFromIDListA" (ByVal Pidl As Long, ByVal pszPath As String) As Long
Private Declare Function SHBrowseForFolder Lib "shell32.dll" _
    Alias "SHBrowseForFolderA" (lpBrowseInfo As BrowseInfo) As Long