Don't be so quick to send it to a garage, this is likely something you could fix yourself a long time before Monday and likely cost you a lot less if you do it yourself. Its really not that complicated, you already have a good idea that its a boost leak, so you are halfway there!. You can hear air leaking, so find where its coming from and stop it, its really is not difficult. The worst leaks to find are the ones you can't hear, so yours should be easy to sort. If you don't want to do a proper boost leak test, run the car at idle, spray soapy water on the pipes by the hissing noise, then blip the throttle, the leaks will bubble.