Hi Nora Charlotte,
I think a lot of people have been in your place, so don't let it get you down. Personally, why don't you ask your girls what they expect from chapter? What ideas do they have? Although you are going to run for the presidency, it is everyone's chapter. Another idea is a retreat....get away for a little while and have fun coming up with ways to build up your chapter....if planned well, those are so much fun. We plan ours for the middle of each semester.
Lastly, I would plan a philanthropy/community service activity with a popular/motivated/nice fraternity. Not only is it a great way to socialize with a fraternity, but if it is done well, you just garnered your sorority some extra good pr, you have a warm/fuzzy feeling from helping someone else, you met some cute fraternity guys and you had a good time with your girls. If that doesn't make you feel spirited and extra-proud of your sorority, I don't know what will. Good luck.