hihi,
I think if you are unable to decide if your gf is the one whom u want to spend your entire life with, perhaps you may want to re-consider carefully again?
You may think that it can be such a "lost of face" in front of your friends or family (if they already know you are going to get married). However, it is better than getting married and in the end preferred your childhood friend or even being single.
Such regret can reach a detrimental state in the marriage and it costs more than a "lost of face" by then.
I would suggest, please have a clear mind and know what you are getting into. It is a marriage and it stands for long lasting commitment.
Emotions can be there for a while, reality will sink in after marriage. There are more difficult things to handle eg. like her mother, her
care-less attitude, unwilling with help you with the chores etc etc.
Hoping that a person will change after marriage, is but a dream.
If you are willing to undertake them and are prepared for the above, then u are more likely to settle down.
However, the fact that u are here seeking for some opinion has indicated that you are having a serious second thoughts which u are unwilling to fact it. I could be wrong. it's just a guess.
I agree with what Milo has suggested that the childhood friend has magnified the problem which has been existing between ur gf and you. u may not end up with your childhood friend.. but cos of her, hopefully u are more clear about what you are getting into.
Take care and good luck