What can i do??

My birthday is coming, i feel like wanna confess to girl that i like for long time on that day..
Actually we already became so flirt in sms , she also knew that i love her since long time ago..
I called her as Bao Bei in sms , but she are not my gf yet
Actually i knew she is giving me chance to become her bf , but i always act like i don't care..
I said i will only request her to become my gf after SPM
Because i am afraid that i can't give her anything if i request her to be my gf now..
But i have changed my mind now..
Because i have realized that i can only be happy when i chat with her
Every bad feeling will lost once i received her message
I am afraid that i will miss out a good gf if i don't tell her how i feel now
But i'm afraid that it will spoilt the flirt relationship that we having
I don't know what can i do now.
Should i take a risk on it or maintain this kind of relationship??
Who can tell me??