You are definitely overfull which is bad for these cars. As everyone said drain some immediately before driving any further. I would take at least 1/2 quart out and check again.
You should reconsider a new mechanic as obviously he's not too familiar with this car.
Just be sure you do not do this.
http://986forum.com/forums/boxster-general-discussions/67165-slight-problem-during-oil-change-what-do-next-3.html