Your original sentence has the right idea, using italics to convey a direct thought. But there's room to make this moment even more immediate and gripping for the reader.
Rather than stating the thought repeated, show it happening in real-time:
‘Vampires are real!?‘ The words slammed into my mind again and again as I raced down the corridor, the snarls of beasts echoing behind me.
See how this puts us right in the protagonist's mindset as the shocking thought crashes over them? Short, frantic phrases and present action beats better convey their panicked state.
Don't just tell us a thought recurred - make the reader experience that repetition. Reveal the thought's actual language to bring us deeper into the POV character's voice.
And balance thoughts with visceral actions - avoid big blocks of italicized text. Blend the physical with the mental to create an engaging rhythm.
Really inhabit your protagonist's perspective. Make their thoughts and reactions feel happening right now rather than just described. This immediacy and blending of inner and outer action is key for immersion.