Heat oven to 350°F. Prepare cake mix according to package directions and divide evenly among three 6-inch round cake pans. Bake at 350°F for 30 minutes. Cool 5 minutes in pans; invert cakes to wire rack and cool completely.
Meanwhile, in bowl, blend marshmallow creme and 2 cups of the confectioners sugar. Knead in remaining 1 cup confectioners sugar. Set aside 1/4 of dough. Evenly knead yellow food coloring into larger dough piece, dusting with more sugar, if needed.
Trim cakes level. Freeze one layer for later use. Stack remaining 2 layers with 1/4 cup lemon curd. Spread 1/2 cup lemon curd on top and sides of cake. Roll yellow dough in large circle (about 12 inches). Drape yellow dough circle over cake, smoothing with hands (there will be a seam). Trim dough to fit, pressing seams together. Roll out untinted dough; cut into assorted-size flowers with small cutters. Tint canned frosting pink with red coloring. Pipe circles for centers onto cut-outs; fill in with frosting. Glue flowers to cake with lemon curd. Wrap cake in plastic; store in refrigerator.
