what make and model printer is it ?
some of them need to select a specific paper type to allow borderless and some cant do borderless at all.
that one really should do it.
heres a shot in the dark. are you printing to 5 x 7 or 7 x 5
the printer sees those as totally different sizes. and it would account for the stripes on only one direction. its trying to print 5 inches on a 7 inch side and so leaves an inch on each end. the other direction may have cut some off but you didnt really notice because your looking at the stripes.
try putting the paper in the printer the other direction just for fun
another possibility is that the picture just isnt large enough to fill. have you tried more than one picture and / or making sure the "fit to page" is checked.
i can offer to log in and look at it with you remotely.
from what you have said i cant see anything you are doing wrong.
but i might see something pop out at me if i was looking at your screen.
mostly i would need you to accept the offer. after that i can get you my phone number and a link do download remote software and we could make an appointment for anytime convenient for you tonight or tomorrow.