The darkness of the picture makes it difficult to see your tree. From what I can make out I like what I see. After it settles in and you are sure it will live you will need to thin down the top of the foliage. Also some companion plantings, moss, miniature azalea or grasses will complete the planting. Should turn out really nice on a slab. But be patient and get it healthy then next spring refine the juniper.