In advance: Using patterns, make the following Color Flow pieces: 6 large and 6 small side panels, 2 small and 1 large arched background panels and 1 cross. Make extras to allow for breakage; let dry. Add details in full-strength Color Flow as follows: For small side panels on top tier, pipe tip 4 scrolls; over pipe with tip 2. For large side panels on bottom tier, edge scallop areas (shown in pattern) with tip 362; over pipe with tip 4 strings. Add a row of tip 3 dots above scallops and tip 4 balls at scallop points. For all arched background panels, outline with tip 362. Add tip 4 scrolls; over pipe with tip 2. Let all pieces dry.
In full-strength Color Flow, pipe tip 4 spikes on back of side panels; pipe tip 3 dots on 11 flower spikes. Attach lollipop sticks to back of cross and background panels. Let dry.
Ice 1-layer 15 in. and 2-layer 9 in. cakes smooth in buttercream and prepare for
stacked construction. With toothpick, trace arch pattern 3 times on each side of 9 in. cake. Outline with tip 362; over pipe with tip 4. Insert spiked side panels into cakes (ends will not meet at corners). Pipe tip 32 upright shell at each corner; add tip 4 dot at end. Pipe tip 32 band bottom borders; add tip 32 upright shells with tip 4 dots. Pipe tip 4 bead top borders. Pipe a tip 32 rosette at corners of bottom tier, insert flower spikes. Insert arched background panels and cross. Attach flower spikes to back of each panel with full-strength Color Flow. Insert 2 lollipop sticks between background panels; position flower spikes on each. Position top portion of heart base; position Communion Boy topper.