You need to cut your back piece and sleeves (long or short) as normal. You may want to add a bit more length as cycling jerseys are typically a bit longer than T-shirts. For the front don’t cut on the fold (so you will have two front pieces) and add half an inch to the width down the middle. You can see the top half of my front pieces in the first photo.
You also need to cut out an extra piece for the back pockets. I used the main pattern piece and cut the shape from the bottom to 7” up for the 4T jersey. When deciding how high you want your pocket piece remember that you will lose almost 1.5” of the height to seams, so cutting 7” high gives you 5.5” high pockets.
Also, cut two pieces of interfacing that are the height of the middle of your front pieces by 1” wide. Iron these onto the wrong size of your front pieces.
We will cut the collar (and collar interfacing) in a later step. You will now have the pieces show in the second photo.