I was terribly shy as a child and became more outspoken over the years. To be honest, the biggest thing is to find your sense of humor and embrace that. For example I have a very precise way of describing the absurd, which works because I'm quite expressive. But many INFPs seem good at goofy explorations and zingy rants.
I'm all for a bit of posturing every now and then, but I agree with others that your sweet side should also be accepted. There are days when my INTP bf is having his nerdy rambles and I'm just kinda listening. If I were outgoing all the time I think that would just be too much for him.