Depends...
Do you want to get serious with this girl? If you have gone out only a couple of months since you made it official.. i would wait...
In my case though, i have only been with my GF for almost 2 months now..
Hahaha shit..
I told her i loved her after one week we have been exlusive.. crazy..
But we have had something going on for like 4 months but didnt made it exlusive with her yet cause i live 1500km away.. and we have been in touch for 1½ year though..
Still, after one week.. it was crazy..
What happened?
Well she was over joyed... really happy.. and she tells me she thinks about that day everyday.. Yet, when i told her, she said she needed some more time.. I just said okay.. And havent told her i love you since then..

..But she thinks about it everyday and so on.. so im 100% sure next time i visit her.. she will tell me first....
Its also a problem with the understanding of the word "I love you"
In english you say i love you to friends, your wife, GF, your mom..
But in other language such as spanish, french and italian.. you say "Ti amo" Only to your GF / Wife!.. And so normally to immature relationship and families and friends you say "Ti voglio bene" which means "i like you"..
So its a question about culture too.. Where are you from?
Im from italy and i told her "ti amo" which is i love you, but the strong kind.. so...
But still.. I dont regret saying it and she loved it so.. I was lucky
But she drives me crazy and i have not regret anything..
sorry long reply