Please help me activate my paid gift card?

Review the information provided here:

If you can't redeem your Apple Gift Card, App Store Card, or App Store & iTunes Gift Card - Apple Support

Do you have the purchase receipt?

If it says the card is not activated that will probably be what matters the most. Without the receipt there is no way to prove you paid for the card and the salesperson could have just took your money and did not ring anything up. That would be an investigation that Walgreen's would have to do and most locations will have cameras pointed at the check stands that are also used to monitor their employees. The registers also records every transaction, so it can be verified if it was actually rung up.