Marriage should is done with both partners’ agreement. Talk to your girlfriend about this and make her understand that you are not ready for marriage. Make her understand that you both had sexual relations with consent and you weren’t the one who forced her. Now, she also shouldn’t force you into marriage. You need to know her mindset and take action accordingly. And if you are unsure about this, then you can ask her to give you some time to think about it and give an answer.