ETA 2451 Full Cleaning - Where did I go wrong? 900 sec slow

So I have a watch with an ETA 2451 that always ran erratic with low amplitude. I finally got around to cleaning it. Complete with new mainspring. Re-assembled and had great amplitude at around 270 but it would not track on the timegrapher. Turns out it was running super slow (I had to put on the second hand and check with a chronograph). I set it all the way fast and was able to get it to register around 900 sec slow. Problem was: I was all the way at the end of the adjustment. Slept on it overnight and simply swapped out a junk 2452 balance and it tracked. So it definitely was the balance.

1. Did I do something to lengthen the hairspring?
2. Was the hairspring always out of whack?
3. Did the previous owner replace with the wrong hairspring and never regulate?
4. No, it's not magnetized ;-)

I'm stuck in a corner on what could have gone wrong. Any help is greatly appreciated.

Signed,
Miffed

It was a kick between the legs. Get it all assembled and looks to be running perfect with great amplitude but get the --------------- /s on the timegrapher display and not be able to adjust it in. Swap it out with an uncleaned junker and get 250 amplitude that I can dial in right in the middle of the adjustment range.

It's just something that has never happened to me before. Can the balance swing too far without overbanking? I see where the slug on the hairspring can be adjusted in and out a little but I didn't touch it and the set screw was tight.

How much space is there between the regulating pins?

Here is the balance. Already have the watch back together. Possible that I simply needed to adjust the hairspring lug in a little to slightly shorten?
Crappy pics. I'll work on better.

Here's a better one

Another top view

uh oh. Just saw the bent hairspring in the pics. This is the problem?

It was running beautiful is why my head hurt. When I swapped balances, the problem was solved. I'm convinced the issue was with the hairspring. You notice that it is slightly bent which would possibly advance the fulcrum forward (lengthen) out of the adjustment range. It still looked fine when static (from the top). I'll play with it a little bit more when I have more time.

I've seen it and it usually disforms the overall shape. This one is still beautifully round. Simply didn't check. It happens.