I feel like I am in a similar place. Rejected to 3, waitlisted to 2, no news from 3. As an undergrad I did had conferences, a publication, an honors thesis, and presentation under my belt. I was feeling a bit confident but then rejections are starting to roll in. Usually, it is about fit. In your SOP you have to make sure you are driving the point of why you fit in this particular program and why that particular program is unique for your needs, research, and future prospects.
Don't take the rejections personally, sometimes it takes 2 cycles to get in instead of 1... I know it sounds horrible but it has nothing to do with your intelligence or ability to produce scholarly work. Sometimes, the application process is just this random thing and becomes similar to winning the lottery. Think of it in Hunger Games fashion, you can increase your chances of getting called but there is no sure way to be called and the person who could be lacking would be the Primrose and get lucky (well unlucky in comparison to the reference but I think you get it).
Best <3!!!