I took off my retainer and it got stuck on my tooth while i was lifting it up. i now have a white line mark inside the enamel of tooth with no scratch outside. will it get healed on its own?

Decalcification?: It may not be related, at least to the event you mentioned. It might well have been there before. Perhaps from decalcification around your orthodontic brackets. Are you keeping your teeth clean by brushing and flossing every time before you put your retainers on? Ask your dentist to take a look at it and see what's going on. It doesn't sound like anything too serious.

Demineralized tooth : Likely demineralized tooth structure, have your dentist or orthodontist look at it to see if remineralization therapy or a filling are needed.

Doubtful: It is unlikely that the mark on your tooth was caused by the retainer. You should have the tooth looked at and have the retainer adjusted so it won't get stuck.

Not the removal: Your question sounds like it relates to what may have happened during treatment or even before. The white mark could be decalcification- a result of bacterial acids or incomplete calcification of the crown of the tooth while it was forming. Ask your orthodontist if there are photos of the tooth before treatment. You'll both know more.

No: Teeth do not heal themselves. White line could be normal enamel that reflects light unevenly, or it can be decalcification, where accumulated bacteria have damaged the tooth surface. Retainers don't cause this, improper hygiene does. Please see your Orthodontic Specialist for review of the situation and to check the "fit" of your retainer. Referral to your General Dentist may be in order.