This is why you have to work from the centre line and not just put the brackets on the tubes. You would be better to make a simple jig that sets the correct alignment of the brackets then bolt brackets to this then put the tubes on.
if you have one side toeing in or out it will cock the whole thing up and will handle like a sack of spuds on a skateboard.

tack a tube on the centre line, use a scriber to scribe centre line and always work from that