The sweetheart roses used are a little deeper pink than the "blue" standard rose.
This adds some nice color contrast and doesn't allow the monochromatic (same color shades) feel too boring.
Between the different flower varieties and shades of pink and lavender, this nosegay has taken on quite an attractive combination of color and texture.
Continue to fill in with the remaining roses until you are satisfied with the look.
Balance the each flower with similar one (or size) on the opposite side).
Sometimes this is done with one standard rose on one side and a cluster of sweetheart roses on the other.