It’s a crazy idea, but disguising yourself as a new student might be your best bet. Disguising yourself as a girl might let you talk your away into your sister’s birthday party and by extension being able to stay for the sleepover.
You’re going to have to put on a convincing disguise though. You can’t just put on anything. You remember that your neighbour down the street is having a yard sale, and that she’s a big collector of clothes from all around the place. That’s probably the best place to find something.
You make your way out of your house quietly, taking care to not alert your sister that you’re planning anything. You then proceed to make your way out to the yard sale without incident.
The sale seems mostly finished, most of the items having been picked up already and the only the owner waking around beginning to tidy up. However there are still a few piles of clothes lying around.
You begin to look over when she notices you “Oh hello there dear. You looking to get some new clothes something?”
Not wanting to reveal what you plan to do, both our of embarrassment and also to prevent her from stopping you, you simptl make up an excuse “Oh uh, not exactly, just getting something for a friend.”
“Oh okay dear. I’m about to head in anyway, so feel free to take whatever you want.”
“Really?” You ask surprised.
“Of course, we’re neighbours after all. Plus these weren’t going to sale anyway, you’re probably the only want still out here right now.”
“Thank you.” You say, glad you’re not going to have to give up your allowance for this dare.
“Don’t mention it. Now excuse me but I need to go do some work.” She says leaving you alone with the pile of clothing.
Looking down you pick something out. You find a collection of clothing from all around the world.