Is it ok to say "yes" to a marriage proposal if you aren't sure when he pops the question?

I have a very strong feeling that my boyfriend will propose soon. He has taken me to look at rings, he is changing things in his life to make our relationship easier if we were to get married, and he even makes jokes about it. We have never really talked about it. I am not sure if I am ready to get married right now, but that is what an engagement is for, right? I figure I will say yes and then during the engagement time see how things develop. If things are good and it feels right I will marry him. If things don't feel right I will tell him I am not ready to get married or end our relationship. Is this wrong?