I don't think this is a serious problem. 

Did you mention when you will start your trip? Since that is the most important criterion customer support use to prioritise requests.

You can leave your pass non-activated until you start your trip, so they can make the change. If they don't get to it, don't worry too much and just start your trip.

(I just use my first and my last name. That's already long enough...)

What do you mean by ´3d name?

There is a kind of official statement that first names are shortened till only 1st letter, then comes famliy name-Spaniards  mostly have 2 family names, most others not.

IF-and this as such is even quite rare (did not happen to me at all using a 10 d in 2 m pass ending last week)- they check its mostly for nr of ID/passpt