I have sometimes bought flight centre vouchers from gumtree and booked cheap flights that way.
Simply find the cheapest flight you can get. Note down the details. Ring your closest flight centre, ask them to book those exact flights, pay using your gift card which gets you 10% off.
I've tried it before with low cost airlines and they never have an issue booking it.
The only disadvantage may be not getting your complimentary travel insurance on your credit card.
Good luck.
Just wondering, on the photo of the card it says +$7.50 issuing fee, what's that exactly?