Boyfriend is mad at me. How do I resolve it and obtain forgiveness?

I accidentally opened a message on my boyfriend's phone. I was borrowing his phone and my finger accidentally tapped it when it popped up, so it opened. I was afraid he'd get mad at me for "snooping", so I just deleted the text. I thought he wouldn't find out. SOMEHOW he did. He somehow knew I deleted it and emptied the trash file to cover it. Now, he's furious with me, calling me a liar and saying I deleted stuff from his phone on purpose.

I told him I was sorry and should have just left it instead of deleting it. I told him I only deleted it because I was afraid he'd accuse me of snooping and purposely reading his messages (he's accused me of "snooping" before when I haven't). I told him I had accidentally opened the message and knew I couldn't make it new again, so I panicked and just deleted it. He said he knew all about it so it didn't matter. Just that I lied and didn't say anything about it.

He doesn't seem to believe it was an accident and I knew I was wrong and shouldn't have just deleted it. I should have kept it there and just told him sorry, but I accidentally tapped this when it popped up, promise I wasn't snooping. But he is still really mad.

What can I do to fix this?

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by the way - the message was not important. It was harmless. I just got nervous he'd accuse me of snooping again and get mad at me, so I freaked out and deleted it like an idiot. I never knew he'd find that if I deleted it and cleared the trash file. How could he discover that info? I thought deleted messages on text were gone.
Boyfriend is mad at me. How do I resolve it and obtain forgiveness?
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