Accidentally made my fiancé depressed by faking my death for a prank and I think she might be traumatized

I (M25) just got engaged to my fiancé (F25) a few weeks ago and my friends and I thought it would be funny to fake my death for a prank at a party. This party was a party at my friends house and had 8 other people. We thought it would be funny to pretend I fell off the roof of the house and died so my friend put on fake blood coming from my mouth, ears, and nose. He then threw a backpack full of books and dumbbells off to make a sound, as I was on the ground already laying down in the yard on concrete. My fiancé was inside the house but near the yard entrance and heard the huge sound and fake yelling of my friends and came out to look and I was laying down with fake blood on me and my friends were saying I’m dead so my fiancé started screaming and crying and shaking me. It goes on for about a minute and she’s on top of me crying on me and I get up and laugh and she screams but I think she was confused and she still thought I fell and hurt myself and we tried to tell her it’s fake but she kept thinking I actually hurt myself. She eventually calmed down a bit and told everyone we’re leaving and my fiancé was in distress still so I drove her home. She was crying in the car asking me why I would do that and I felt really bad for her.

That night when we were sleeping she woke up screaming because she had a nightmare I died.now she doesn’t really get out of bed unless it’s for work and she doesn’t like it when I leave her sight because she’s worried something will happen to me. I think she’s psychologically shocked or damaged and I don’t know how to help her. I wish I never did that stupid prank I cry every night in the bathroom because she’s suffering from my stupid mistake I thought would be “funny”. We are going to the therapist next week but I don’t know how to help her in the meantime. I just want her to be happy again