Fixing a (probably) 3D printed headphone holder?

My gf bought this holder off Etsy. Before I could mount it the keyhole bracket came off. It was glued on but not very well. Should I use a certain epoxy on it? The inner edge seems to be too narrow to use the two screw holes to hold it on but I could try with a screw/nail? Any advice is appreciated!

My gf bought this holder off Etsy. Before I could mount it the keyhole bracket came off. It was glued on but not very well. Should I use a certain epoxy on it? The inner edge seems to be too narrow to use the two screw holes to hold it on but I could try with a screw/nail? Any advice is appreciated!