VAT refund rookie

I've looked up a lot about this but it all just confused me more. I'm an American and I've been in Scotland for a month. My law of the EU professor here told me that I could take my receipts to the airport and get 20% of the purchase price back because of VAT. I've got about £300 of purchases from various places (about £50 each) and I've got all the receipts, but I don't have any VAT forms. I leave from the Edinburgh airport tomorrow morning. Is there any way to get the VAT refund or am I just out of luck this time?