Preemie weight gain

Hello mommies ! I have a 34 weeker who is currently 13 weeks old actual age. Her birth weight was 3 lbs 11 oz and she is currently 8 lbs 6 oz. is this a good weight gain ? I know each baby grows differently but want to know how your preemie babies gained ? She is fed on breast milk through a bottle . I also fortify my breast milk with Neosure based on what they told me at the NICU.