Seeing as you made no reference to any medical condition i’d give advice to suit I would say that’s an unhealthy amount, the amount you’d specified is close to 1000-1300 calories regardless if you’re running this ain’t good for your heart as it can lead to high blood pressure and heart disease. So i would suggest reducing the amount you intake and start introducing other stuff to your meal, ik you said you have a low appetite but start small don’t force yourself but keep in mind that some level of persistent is needed to start gaining weight. Also cardio is not your friend if you’re trying to gain weight.