I got seduced while tied up by my friends little sister

So I was 25M at the time and at university doing a filmmaking course me and my friends were making a horror film we used our friend Joe’s [25M] parents house he is from a very conservative Chinese family and their house looks like a time warp from the 50s minus all the fun rockabilly decor. His parents were away for the weekend so we used their bedroom it had this really old double bed with poles and curtains etc on the side of it. We were filming a torture scene and the actor for that scene cancelled so I stepped in, stripped down to my boxers and got tied to all four poles of the ped we filmed a few shots and Joe and the guys thought it was funny to leave me tied up while they went downstairs out into the garden to smoke up, we always play pranks on each other so I was laying there tied up. Joes younger sister Rosie [18F] walks past with her boyfriend they both laugh at me, he’s on his way out she kisses him goodbye then walks over to me she’s giggling making fun of me and I ask her if she wouldn’t mind untying me she says “why? I’ve finally got you where I want you” she rubs her hand along my thigh” I glance over to the window I can hear Joe and the guys chatting outside etc and I say “what are you doing?” She then starts tracing her finger along my boxers.. she’s very pretty and has an incredible figure like slim but decent sized boobs etc I can feel myself getting hard and she notices giggling but I’m also terrified Joe is a bodybuilder he would beat the shit out of me if anything happened so I said “very funny ok just untie me now, I’ll call Joe if you don’t stop” then she pulls back my boxers my 9 inch thick white dick springs out “you’re like more than twice the size of my boyfriend!” And I’m stuttering as she spits on it and starts stroking “I don’t think you want me to stop” and I grunt looking out the window “this feels so wrong but so good” she says “look at me not out there” she starts slowly sucking my dick and although im tied up i start thrusting in her mouth calling her a slut then she stops gives my dick a light slap “no no, you’re not in charge here” and I apologise she says “it’s okay that’s made me wet, okay warn me when you’re close okay” she climbs onto me mounts my dick and starts riding me we keep glancing out the window and then we see them starting to walk inside I say “quick go go” she climbs off but then starts hungrily wanking me off against her tongue whispering “give it to me” I cum so hard she catches it all in her mouth pulls up my boxers and hides in the wardrobe she then jumped out in the middle of filming pretending it was a joke Joe had no idea what happened before that