Is hijab obligatory?
Short answer: Yes. Allah commands believing women to cover themselves with their outer garments and head coverings in front of non-mahram men.
Allah says: “O Prophet, tell your wives and your daughters and the women of the believers to bring down over themselves their outer garments” (al-Ahzab 33:59), and: “Let them draw their head-coverings over their chests and not display their adornment” (an-Nur 24:31). Covering the body is an obligation upon the adult Muslim woman in front of non-mahram men. The scholars differed about covering the face, and many scholars of Ahl al-Sunnah held it to be obligatory.
Answered according to the Quran and authentic Sunnah as explained by the scholars of Ahl al-Sunnah wal-Jama‘ah. For your own situation, ask a trusted scholar.