Got a gift card for christmas, loaded it all up to steam and now it wants me to verify it, but I don't have funds in my account to. Need help

I got a $50 gift card for christmas, not Steam specific, just a normal gift card, and now it wants me to verify it but I can't because I used all 50 on steam. I wanted to do a case unboxing and now I can't buy any cases on the market. Anything I can do?