It is OK to send 11 roses or 19 roses, depending on the meaning of the different number of roses and the emotion you want to express.
For my lover, it is best to choose 11 roses, which means that I only love you for a lifetime. You are the person I care about most in my life. When you express your love to someone, it is best to send 19 roses, which represents the expectation of love, expressing your true heart, and is also suitable for marriage proposals.