That promotion might be this one, or something similar:
Back to School - Terms and Conditions - Apple
Quotes:
"Qualified Purchasers who purchase an Eligible Product through a Qualifying Location during the Promotion Period shall receive a discount equal to the value of the Promotion Product (depending on their purchase, as set forth in the chart below) off the price of the Eligible Product at the time of purchase. Customers will be charged for all items in their cart, including the Promotion Product."
So they're giving you a $150 discount on the laptop, then charging you $150 for the gift card. IF you keep both – and think of the laptop as having been sold at full price (not the "price with special offer") – the gift card is effectively free. But
"The Promotion Product is redeemable for future purchase(s) only and is not a “gift.”"
and
"The Promotion Product received with the purchase of an Eligible Product must be returned with such Eligible Product in order to receive a full refund for that purchase. If the Promotion Product is missing, is not returned, or has been redeemed, the full original value of the Promotion Product will be deducted from the exchange or refund of the Eligible Product."
So you can't return the laptop (only), or return the laptop and a used gift card, to get a "free gift card". If you do not keep the laptop, they're going to get the $150 back one way or another.