That said, there is some really good advice here. You do need to upgrade your gear and do a little research on what stats you should be looking for. You have whites equiped and other items with stats that are of no use to a mage.
In an instance, remember that you are part of a team, it isn't just 5 individual players doing their own thing. As DPS you have a specific task and as a mage, there is a specific way to accomplish that task. Again, do some research as that's the best way to get a better understanding of how to play your class.
If none of that works, shrug it off and queue up again. Trial and error.