Adjustment of Status - I-485

First thanks for reading my post and appreciate your advice and guidance. I came to USA in a very young age and now I will be marrying my long time girl friend for 3 years, who is a citizen. We both are from different countries as well. She is from Mexico, but born American citizen and I'm from India. We will be doing a court marriage first, in the end of this month, since she wants to get married in Mexico. Off course, our parents are against this marriage so this is why we will be doing a court marriage. She is catholic and I'm Hindu.
Now the question is, how to proceed further? I came to this country on a B1/B2 visa and over stayed since then. I read some scary stories on the web about the scary interviews. However, I'm not least worried about this, but nervous since how can one know another person so well. It takes forever to learn someone who you love. Also, She is staying with me and the lease is under my name, and have pictures. But I don't have any bills under her name yet, since I pay for the cable. And since I don't have a bank account, she handles my cash in her account.
How can I proceed without giving the immigration officer the benefit of doubt. A good response will be highly appreciated. Thanks in advance!!