Hello, My Girlfriend And I Had Unprotected Sex Last Week

Hello,
My girlfriend and I had unprotected sex last week on Thursday and my penis poked in her anal by accident. On friday morning when I checked my penis it had a small red bump on the tip near the urethra, there's no pain or itching. Now today it appears the bump is growing a little bit. We both got checked before having sex and we don't have anything.
Can someone please help?