I (28F) accidentally ruined a Christmas gift from my husband (30M)...what now?

I accidentally saw a Christmas gift my husband of 8 years bought me and it is something I wanted that was quite pricey. But...he ordered them in too big of a size. He ordered this on ebay (which is how I saw it by mistake, we share an account) and the seller has a no returns policy per their account.

I am not sure what to do. Do I let him know ahead of time or do I wait for Christmas day? Do I sell them and get the size I need? No idea what to do. Trying not to be too specific but they are shoes for a sport that I do and I can't use them if they aren't my size.