Hehe, bride-to-be, I have attended many weddings, and I feel that if I have prepared my lines before, the overall effect will be fake, and it is not necessarily that you are too nervous to speak on stage. So I suggest, don't prepare anything before, just play it on the spot, even if it's just saying I love you, just three words. If you think it is necessary to have a manuscript before, then you can talk about what touched you most about the groom, or you can say that after all that, you completely decided to marry him, and so on.

Although I am not married, I hope my answer will help you, and I wish you a happy wedding!