The last day of my period was on December 19th and I had sex on December 23th what are my chances of getting pregnant

The chances of you getting pregnant all depend on when you ovulate. Since we don't know that, it is impossible for us to tell you whether you were fertile enough to conceive.

If you are not trying to get pregnant, use protection. Preferably 2 or 3 methods since protection can still end up in pregnancy.

You are now playing the waiting game. You will have to see if you get your next period. If not, be sure to test using first morning urine.