"Can I file more than one return after paying the $39.99 fee online for turbotax?"

TurboTax Premier includes a single return, with additional returns available at a cost of $19.99.

But at Staples I paid for 8 returns

There is a purchase of the online Standard edition for 8 returns or you can get the downloaded version as well. This means that at the end of each return you enter the prepayment code provided for up to 8 returns.

The link below will assist:

• In the online edition of TurboTax, how do I use a prepayment code?

At the review stage of your tax return just before filing, you will have the screen presented below to enter your prepayment code: