Have you got the shipping confirmation for your order? If not, try contacting Google Store support: https://support.google.com/store/answer/7334136?hl=en
If your order has shipped, you should get your activation code after getting the shipping notice. You can contact Stadia support via https://support.google.com/stadia but they will likely tell you it may take 3-5 business days and to contact them again if you still haven't received the code by Friday.