Instead of black jeans, wear black dress pants. Also, swap the vans with a simple black slip on.
You must think to replace the jeans for something else. For example a grey midi skirt can be a very good option.
Violet, I'm not sure, but I'm think your talking about 8th grade promotion, right? Well, prior to that question I think your planned outfit is not appropriate for the occasion. Yes, the white blouse and black cardigan is nice, but jeans and vans….for promotion? How about you wear the blouse and cardigan with a skirt and flats, and just maybe vans will do. (: Congrats Graduate!
Yes.
You do not need to wear a dress. The blouse and cardigan are nice. However jeans and vans are not appropriate for graduation. Slacks and flats would be a better choice. If your school allows leggings, you could wear leggings and flats with your blouse and cardigan.
I think you should find a skirt or dress that is your style and makes you feel comfortable :)