Speaking up does not require a perfect or completely proven idea. It requires a useful contribution. Structure an idea as observation, proposal, benefit, and question: what you noticed, what you suggest, why it may help, and what response or test you want from the group.
Confidence comes from clarity and preparation, not pretending certainty. Label an early idea accurately, support it with the evidence you have, and name what still needs testing. Questions and objections can improve the proposal; listen for the underlying concern before defending your original wording.