You have not heard the good news obviously.....tremor dominant PD progression is slower than the rigidity type. If you have played guitar for years the tremor won't really interfere for a long time. PD tremor is a resting tremor so once you get the old fingers warmed up you should be good to go.
DO NOT - I repeat DO NOT take extra PD meds to compensate for any perceived problems with tremor. If you are feeling a bit anxious about playing in public with PD get your Dr. to give you an anti-anxiety med. Save your sinemet for the big bad days ahead. Have you read the threads on sinemet use Start with the current one by Fiona (blog about sinemet) then look back a bit for one I started called "Is sinemet addictive".

Congratulations on the gig...may you play happily for many years to come!