For future reference, the most secure option would be to fuse the little heart to the big heart (I like WonderUnder, but H&B would also work) and then satin stitch the little heart, then fuse the unit to the background & satin stitch around the unit. Pinking the edges will not help & might, ironically, actually cause slightly more fraying.
If your machine does a blanket stitch, you could also do that & it would be very secure. I did blanket stitching (by hand because I have an old machine) on my niece's quilt & it has held up fine through dozens and dozens of washings. The fraying happens when you have a wide stitch. If you use fusible & tiny stitches (I aim for a scant 1/8" wide & 1/8" long on my blanket stitching), the raw edge will barely fray at all.