Since you will be serving this at an event, there should be no trouble dropping the pressure to serve. You want to repressurize anything that's left over if you intend to store it.
Since venting pressure often leads to making a mess, I like to turn off the CO2 completely and let the existing pressure serve the first few pours. On a full keg with small headspace, that shouldn't take too long. Once the pour is pretty slow, turn the CO2 back on, but start at 5psi and turn up as desired from there.
Longer lines will help, but you're not likely to have that in operation by Tuesday unless you have somewhere local that sells the proper sized lines.
Other solutions for future reference would be to get a narrower diameter and/or longer serving line, inserting epoxy mixers or other line restriction in your dip tube, carbing/serving at lower temperature and pressure.