I once heard someone say "marriage is an odd thing, you may not always know if it's right, but you will often know if it's wrong". From the sounds of it you're not ready for marriage, and I know it sucks but it's important that you tell this to your girl. The truth is that yes, you can get married, or you can even just put it off, but if you marry her without being ready for it you're likely to break her heart in the end and if you just put it off you're getting her hopes up. It's important you tell her this, help her realize that by telling her this you're trying to make things right, doing anything else will just hurt her.
