Mazal tov on your upcoming marriage!
You may start a second pack of pills without a break before your wedding and continue taking active pills until after you have consummated the marriage (and become niddah through dam betulim). You do not have to complete the second pack. Instead, you should stop them the day after you have had intercourse and let your period come.
This short-term use of birth control pills to avoid niddah at the very beginning of your marriage is halachically permissible, even though it means you will not conceive the first time you have relations.
If you have never extended your cycle before, there is a concern that you may experience staining during the extra days of active pills, which may cause an issue with counting the 7 clean days before your wedding. If your wedding will take place within the next month or so, you may follow the advice above, but we advise reviewing our articles on stains. If you have a few months before your wedding date, it may make more sense to slowly shift your period over the next few months, adding a few extra days of active pills to each cycle so that it will have adjusted in time for your wedding.
Please feel free to get back to us with any further questions.