Welding Tips and Tricks

Howdy,
Replacing a section of deck on my steel yacht. The deck beams are 2" flat bar (vertical).
The deck camber requires the flat bar be bent, about a 5mm camber. I couldnt get the things bent by anyone so I made a jig outa angle, channel and some round bar and a bottle jack.

Strangely, altho' the position of the jack was measured and centered smack bang in the middle, all 3 beams favoured the left side.
so I have deck beams of vertically placed flat bar with more camber on the left than right.
I'll have to do them again of course :
SO I WAS WONDERING IF ANYONE HAS A SIMPLE METHOD OF ACCURATELY BENDING A SLIGHT CAMBER ON VERTICAL 2" FLAT BAR?????

LET ME JUST ADD:
It appears the flat bar bent more to the left due to grain structure perhaps.
I wont waste time trying to correct the bad bend, just start again.

If you require a slow curve over the entire length on edge the reliable method is make a simple roller bender - there are many on You Tube with good build instructions - if you can get away with a series of bends with flats between it's easy to cut part way through the 2" with a slitting disc at regular intervals bend the piece by hand in a vise then weld the slits up which will now be small V's .