That would depend by what you mean by didn't enter completely and also where in your monthly cycle you was.
As with any unprotected intercourse there is a high chance of pregnancy even if he pulls out and doesn't ejaculate inside you.
You should always use condoms not only do they help prevent pregnancy but they also help prevent the spread of STIs and STDs what can have life changing effects and can also leave a woman unable to have children he not treated soon enough.
Do you mean he pulled out before he ejaculated when you say not complete?
If you have unprotected sex then there is always a lot higher chance of pregnancy than he you use contraception. You may not show any symptoms as some don't but you can Google pregnancy symptoms to find out what the are.