Visual Studio 2012中的WriteAllText帮助

所以我有一个正在使用的程序，我需要读取.ini文件的行，然后将用户定义的文本写入该文件中的特定行。到目前为止，我的一些代码是：

Dim File As String = ".\TestFile.ini"
    Dim FileText As String
    Dim NewText As String = TextBox2.Text
    Dim lines() As String
    Dim separator() As String = {Environment.NewLine}
    Dim x As Integer = 0
    If My.Computer.FileSystem.FileExists(File) Then
        FileText = My.Computer.FileSystem.ReadAllText(File)
        lines = FileText.Split(separator, StringSplitOptions.RemoveEmptyEntries)
        While x < lines.Length()
            If lines(x).Contains("Nickname") Then
                lines(x) = "Nickname" & "=" & TextBox2.Text
            End If
            NewText = NewText & lines(x) & Environment.NewLine
            x = x + 1
        End While
        My.Computer.FileSystem.WriteAllText(File, NewText, False)
    Else
        MsgBox("File does not exist!")
    End If

我要编辑的文件如下所示：

Don't edit this line
Don't edit this line
Don't edit this line
Don't edit this line
Nickname=test
Don't edit this line
Don't edit this line
Don't edit this line

我只想在第4行上编辑此单词“ test”，但是我执行的代码会执行此操作，但还会在文件开头添加我在TextBox2中输入的内容。像这样（假设我将HelloWorld放在TextBox2中）：

HelloWorldDon't edit this line
Don't edit this line
Don't edit this line
Don't edit this line
Nickname=HelloWorld
Don't edit this line
Don't edit this line
Don't edit this line

有人知道我的代码有什么问题吗？抱歉，我对此很陌生。