the background image code i have does not resize the image for you. if your image was originally too big it will appear big/the same size in the background and if your image was too small, it will appear small in the background.
so i recommend first try replacing all the quotation marks in the code i provided in the answer (cuz usually that makes all the difference) and then if there is a resizing problem try another image.
if it still doesn’t work please ask again off anon so i can see what the problem is.
thank you and good luck!