Student or Learner
Do both the sentences look comprehensible but not awkward to native speakers?
Situation: I saw something surprising, so I felt surprised and looked surprised. I just couldn't pretend to be expressionless.
(1) I couldn't help but have a surprised look on my face.
(2) I couldn't restrain a surprised look on my face.
In addition, is "on my face" a must in the sentences?
Example sentences in dictionaries all include "on one's face". (I believe it's because "look" has many meanings, so "on one's face" is written to avoid misunderstanding. But is "on one's face" really necessary all the time?)
Yes, I think both are all right. The second is rather academic. I don't think you can omit "on my face" because it would change the meaning to indicate only the expression people see in your eyes.