If you don't have a sewing machine, you could also try the 'no sewing' options of an iron and no-sew tape after you've pinned it in place, or even hot glue in a pinch. But I stress- these should be "plan B and C" options, as sewing is sturdiest and hangs best.
At least it's too big, that's way easier to deal with than too small.
Ohoh, you could also try hooking up a lace-up back--like a corset or a shoelace. That could possibly allow you to adjust for a skin-tight fit in the front (it's easier to be accurate without having to be as precise as taking in the sides). Down-side is it may get all bunchy in the back unless you do it just right. It's a thought, anyway.
