how can I save a chicken wellington sauce that has too much lemon?
To start, here are some ideas on diluting a too lemony or acidic sauce:
If you have already applied the sauce to the chicken etc, it's tougher to fix.
If the sauce is still separate from the other components, you could make another batch WITHOUT acid (no lemon, wine or vinegar), then mix the two batches (the TOO-lemony and the NON-acidic) and use half on this recipe, and save half for another time.
If the sauce is already in the chicken-puff pastry assembly, wait until it's been cooked, taste, and serve with more dairy (butter or cream) to blunt the acid, or plain carbs like steamed potatoes, to absorb it.
Good luck and I hope one of these suggestions help.