Speeding up Macro

I have a Macro I recorded it takes anywhere from 18 to 20 sec to run. how can I speed it up?

Sub TabLow()
'
' TabLow Macro
'

''PURPOSE: Determine how many seconds it took for code to completely run

Dim StartTime As Double
Dim SecondsElapsed As Double

'Remember time when macro starts
  StartTime = Timer
'*****************************



Application.ScreenUpdating = False
    Selection.NumberFormat = "@"
    For Each ThisCell In Selection
    If Len(ThisCell) < 10 Then
    ThisCell = Right("0000000000" & ThisCell, 10)
        Else
        End If
    Next ThisCell
    Application.ScreenUpdating = True

    Range("C1:C1500").Select
    Selection.Copy
    Columns("A:A").Select
    Selection.Insert Shift:=xlToRight
    Columns("A:A").EntireColumn.AutoFit
    Columns("A:C").Select
    Application.CutCopyMode = False
    With Selection
        .HorizontalAlignment = xlGeneral
        .VerticalAlignment = xlCenter
        .WrapText = False
        .Orientation = 0
        .AddIndent = False
        .IndentLevel = 0
        .ShrinkToFit = False
        .ReadingOrder = xlContext
        .MergeCells = False
    End With
    With Selection
        .HorizontalAlignment = xlCenter
        .VerticalAlignment = xlCenter
        .WrapText = False
        .Orientation = 0
        .AddIndent = False
        .IndentLevel = 0
        .ShrinkToFit = False
        .ReadingOrder = xlContext
        .MergeCells = False
    End With
    
     Application.ScreenUpdating = False
Set rg = Selection
For Each cel In rg.Cells
    If Len(cel.Text) = 1 Then
        cel.Value = Val(cel.Value)
        cel.NumberFormat = "00"
    End If
Next
    
    

        
    '*****************************
'Determine how many seconds code took to run
  SecondsElapsed = Round(Timer - StartTime, 2)

'Notify user in seconds
  MsgBox "This code ran successfully in " & SecondsElapsed & " seconds", vbInformation


End Sub

it moves column C over to column A then if NEW column C
is less then 2 digests it add a 0 to the front.

My code works just slow i have attached an example

The reason it is so slow is that you are selecting three entire columns (i.e. 3,145,728 cells). Set rng to only the cells you need to look at, and it should improve speed massively:

    LastRow = Cells(Rows.Count, 1).End(xlUp).Row
    Set Rng = Range(Cells(1, 1), Cells(LastRow, 3))