First, to answer this you need to know how you're supposed to wear the engagement ring and the wedding ring together after the ceremony. Tradition dictates that you wear the wedding ring first so that it is closest to the heart, and the engagement ring goes on top.
So, you can see that if you wore your engagement ring during the wedding ceremony, it would block the wedding ring's proper position.
There are a couple of options of what to do.
You may want to forego wearing the engagement ring during the ceremony, and give it to a trusted bridesmaid or family member for safekeeping until the reception when you can return the bling to your finger. With this option, the focus truly centers on the commitment symbolized by the wedding rings. In fact, in Jewish tradition, the bride and groom are not supposed to wear any jewelry during the wedding ceremony to show that their mutual commitment to each other is based on who they are as people, not on their material possessions.
But if you just can't bear to part with your diamond, many brides simply place the engagement ring on their right hand for the ceremony. They put the rings in their proper order on their left hand after the ceremony.
Either way is perfectly acceptable, so do what is comfortable for you.