You are able to register marriage now. https://mothership.sg/2020/05/marriage-solemnisations-in-person-june-2/
However, before that I would suggest you to think about it and solve the problem between both of you. You should share your feeling and expectations with your boy friend. Is he willing to change as he is going to be a father. He can't be playful and think of himself.
Are you able to accept if he is reluctant to change? What if he is engross in his game and neglects both you and the baby? Are you willing to endure such life? Even if you are willing, it is not right. Is altercation going to be part of daily life? How about financially?
I understand your feeling and may be in dilemma. If is a mistake, should one continue it or solve it before it gets worse? Just my two cents worth. I'm sorry I couldn't give you solution. Hope thing will be getting better for you. Enjoy your pregnancy and be happy. 🌈