Sharp pain in the upper center of my chest. it has lasted all day. could this be heartburn?

Hard to say: Heartburn, inflamed ribs, anxiety, gall bladder are all potential culprits. Since it could be from the heart as well, best to be fully evaluated by a physician.

Less likely: I guess heartburn was named due to the fact it is perceived by many as "burning". Sharp pain is unlikely to be heartburn. I'd look for something like muscle spasm or costochondritis, a painful condition in the area where the bony part of the rib connects with the rib cartilage.