What a cool find! If it's definitely your wish to enlarge it, how about a 30s pale yellow floral 3" border and a brown pin dot binding? That would keep the vintage vibe. Or find some turquoise gingham for border and a red bandana print for binding? If it were mine, I think I'd just bind it. Pick a color you like to "frame" it and keep it solid. I like the muslin suggestions.