In order for us to help you with your question, please provide us a minimal reproducible example where you provide a minimal (dummy) dataset and code that can recreate the issue. Once we have that, we can go from there. For help on creating a Reprex, see this guide:
I assume you have to group and summarise the data before you plot the curve, so please be sure to provide a sample of the original data, and how you'd like to group it.