[mothered]

My plan is to contact support and tell them that when I opened the the box I found a dfferent GPU in it than labeled (my old gpu).

do you think I would be better off just trying to return my old gpu in the 2080 box and hope they do not notice

Why not get/purchase a significantly cheaper Item that they stock (Inventory), weighs roughly the same as the GPU, and tell them you've received that? When they request the return, send that. No problem If they check It- It's a stock Item.