The jam spaces are located on both sides. However, the flowing directions of candies make it extremely hard to spread the jam to the middle part. This is because even though you have coloring candy or color bomb combinations, it is very hard to bring the jam to the middle zone due to the mechanism of the combinations.
Striped candies. Prepare a combination of coloring candy/color bomb and striped candy. (You can use the available color bomb under the ice if you can get to it fast enough). Wait until there are one or more candies of the same color as the striped candy on squares with jam. The combination will turn those candies into striped candies and spread the jam to the center.