If I hit myself in the eye with a scissor but my eye didn't really get red, and the irritation was gone after like 10 minutes, should I be worried?

Not necessarily. If you have no pain and no change in vision, you are probably fine. Was your eye closed? If not and you cut or scratched your eyeball (which can sometimes not hurt), you do need to get seen right away. You also need to get seen if you have pain in your eyeball or blurry vision, or your pupil changes in size when compared with the other.
No Problem. If you're feeling OK within 10 minutes, you most likely didn't damage the sclera or cornea. You should be fine.
Listen to your body. If you had injured your eye seriously, of course, you would have gone to the ER. So I gather it was a low acuity event and you're just worried that something unexpected will happen tomorrow or something. Let me reassure you--eye trauma has no mysteries. Usually the pain and irritation is exaggerated. So let it tear, keep fingers out, flush with water if needed. If symptoms progress go to ER!