When you start the amend process, the refund that is shown in
TurboTax is reset to zero.
You will still get the original refund. The amended return will
show the difference you owe, or that you will get back as a refund (in your
case, in addition to the original refund amount). You will get two separate refunds, rather than just one.
You can confirm this by printing your amendment and looking at
the 1040X. On Line 18 you should find your original refund amount and on line
21 you should see your additional refund. If you paid on your
original return it will be on line 16. If there is an amount owed
with the amendment, it will be on line 20.