It is a serious problem if the bone graft is coming out with the stitches. Some particles of graft (similar to grains of sand) may come to the surface but there shouldn't be complete exposure of the site. If the graft gets exposed to the oral environment too early it becomes very unpredictable.
its my request to upload pic so i can guide u better. because u have to mention what kind/type of graft used. if putty , in that case if stitch is open and graft is little coming out no need to worry [ its over 48hrs] because clot will hold graft material. if u feel any kind of pain in that area visit dentist, indicating infection. otherwise avoid aggressive cleaning of that area for next 5 days.