How far off you might be is hard to say, but like the old saying, "A miss is as good as a mile". In other words when you get the pump back from the shop they should have it timed exactly but, obviously, the engine will not be timed exactly. That being the case, wether your 5 degrees off, or 15 degrees off, or 180 degrees off, the pump will be out of time with the rest of the engine and it will not run right, or possibly at all.
My suggestion would be to pull the plunger assembly and get a new one if the small part on the end is broken off. Too, I have seen them be just be stuck enough that they will not push out and engage the timing hole without literally driving it out with a hammer. In that case, simply pull the assembly and free up the one that's there so it will push in and engage the timing hole like it's supposed to do.
Based on what your saying you did, you ought to be close, so once you have the timing pin situated rock the engine back and forth while pushing in on the plunger til it engages with the hole. Unfortunately that is the only way your going to have any guarantees as to wether the engine will be in time and run when your done.