I would not think that “looking again” at a girl’s face would be anything but appreciative of God’s beautiful creation unless some other factor made it so.
A few things you might consider if this is bothering you: Does this repeated looking cause any degree of physical arousal? Do these looks cause your mind to move towards God’s mystery, the magnificence of his creation, and contemplation of the the spiritual depth of the girl, or are your thoughts (even when not at all lustful) sometimes more objectifying than that, simply seeing the beauty of the girl’s face as a cause for your viewing pleasure? Is there a girlfriend for whom you should be reserving those second looks out of love and affection for her? Could that looking potentially be a minor cause of scandal for those around you?
In all likelihood, you’re absolutely fine with these looks; they sound like they’re totally chaste and nothing but building up of other people. Just keep one eye on your conscience and don’t worry too much about it. We have bigger sins to fry (=.
God bless.