vba多个工作表二维转一维，然后储存到新的工作表，请看看我哪里写错了，它运行出来的数据不全

Sub 转换()

Dim x As Integer

Sheet15.Cells(1, 1) = "门店编码"
Sheet15.Cells(1, 2) = "商品名称"
Sheet15.Cells(1, 3) = "订货量"

For x = 1 To 14
Sheets(x).Select
Dim i%, j%, a%, arr
arr = Range("a1：bb20")
a = Range("a666666").End(xlUp).Row + 1
For i = 2 To UBound(arr)
For j = 2 To UBound(arr, 2)
Sheet15.Cells(a, 1) = arr(i, 1)
Sheet15.Cells(a, 2) = arr(1, j)
Sheet15.Cells(a, 3) = arr(i, j)
a = a + 1

        Next
    Next

Next
End Sub