Dad's pushing for me and my so to get married.

So my dad is now putting pressure on me to get married before the baby comes so the baby come into this world into a stable relationship. He said just do a quick one now then once the baby is born have a proper wedding. I don't want to coz it's to much rushing and just coz we are pregnant people will think that's why we are getting married. Which it wouldn't be but yeah. We plan on getting engaged and married but just don't wanna be forced into like right now. My so knows i dont wanna go to long with having a different last name to my child. So we will get married but in our own time. What are your thought?