You should speak with an experienced immigration attorney. With marriage based immigration, especially with couples who have been together for a short period of time (lets say less than 1 year) there may be a presumption of marriage fraud, even if legitimately in love and ready to get married. An experienced family based immigration attorney will be able to guide you and help you to build the strongest application possible. Part of building a strong case involves finding the right documentation to prove that your marriage is bona fide. You can find many experienced attorneys here on AVVO.com or at AILALawyer.com. Many offer free first time consultations. Best of luck!