I got caught planning to have sex. I'm 17. My mum is upset. What do I do?

Validate your Mom’s feelings (this can be upsettting for many) but also set a boundary that you are almost an adult and allowed to make choices for your own body. Assure her that you will be using protection so as to avoid STDs and unwanted pregnancy. Other than that, not much you can do. It’s okay that she is upset, hopefully she has a good support system that can help her work through her feelings.

Speak to your mother and have a think about if you are ready for this if your not then wait for a while do not rush into anything as it will be hard it is understandable your mother is upset she's worried about you talk it through with her and see if you can find common ground

I think it better to have a conversation with her. Often times parents can be controlling and would project their expectations on us. I think if you have a conversation with her, seat her down, letting her know at the beginning of the conversation that you want to have a genuine talk and not argue, that could ease things. Try to get her to see things from your point of view, then let her speak. Hopefully this conversation can be helpful.