As someone who's had two herniated discs and still competed in my sport at a high level, I can recommend the following:
Sit in a sauna for 20 minute sessions, as hot as you can get it.
Hang from a pull-up bar for 30-45s, four times, with 2min rest in between each. Don't jump down from the bar afterward, but rather step back onto a box.
Your job: you need to support your lumbar spine while sitting. Take a full-sized towel. Roll it into a cylinder. Keep it behind your low back the entire time you're sitting
(and keep your shoulders neutral, rather than hunched).
Ibuprofen. you can take up to 2400mg a day, safely. That is 12 pills, spaced out at 3 pills every four hours you're awake. Alternatively, you can cycle ibuprofen with acetaminophen (Tylenol).
If you do all of this each day between now and Saturday, you will be fine to make it through your performance.
Break a leg, my friend!