If your academic performance is not satisfactory or if you think there is more room for improvement in what you've done, you can say you are feeling '아쉽다'. For example, you expected you did really well on your exam and got all correct answers, but it turned out that your mark was 97. So your actual performance didn't live up to your expectations, you can say '점수가 아쉽다'. However, '섭섭하다' or '서운하다' is used when you are talking about others not yourself or your performances. If your friend did something different from what you are expecting from him or her (not in a good way), you are feeling '섭섭하다' or '서운하다'. It might be similar to the feeling of disappointment. For instance, if you were broke, you might expect your friend to lend you some money. But if your friend flatly refused to give money to you, then you could say '섭섭하다'.