i'd take off that frame and install a new one for that price
that way you'll be able to fit a proper cover on there. covers for wide tanks are usually too small covers
it will most likely look better then a DIY job if you've never done it too.
just rip the top off, remove any sillicone with a sharp blade and put aquarium sealant inside the new cover and put some weight on top of it for 24 hours. that'll stay well in its place