There is no steps you can take now, if your girlfriend does not want to take I pill, and she has every right to make such desicion.
Would you take hormonal bomb to protect anyone from pregnancy and cause yourself possible harm and hormonal imbalance afterwards? No, you would not.
Anyhow, if the both of you are not ready to have a child , I pill is better option then abortion, and certainly wiser option that to have child and not ability to take care about him or her - but treat it very seriosly: use it once in the life and never again. I pill is not harmless, not safe, and it is not contraception. In that case speak to your girlfriend again and try to explain her the situation, she might change her mind and use I pill anyway.
For the future - have protected sex only, if you don`t want to have baby.
If she refuses I pill, and her period is late, you can buy pregnancy test in pharmacy and check it 2 weeks after her period was supposed to occur (what means in the middle of the March).