My mom is thinking about grounding me, but I didn't do anything....please see details?

So I was in my room on my laptop. The door was locked and I had up Google Chrome Incognito, which basically means it doesn't save your history. The reason for all this was because I was ordering a mother's day gift for my mom & I didn't want her to walk in and see or check the history on my laptop and see. She knocked on my door so I closed everything out and opened it. She came in & yelled at me & she now thinks I'm talking to pedophiles online and watching porn and stuff. I don't want to tell her I was ordering her something for mother's day but she says she might ground me for 'lying' because I said I wasn't doing anything, but she doesn't believe me. What should I do? I don't want her to think I was being bad or anything but I don't want her to find out either. Help please ?