It doesn't matter how long you say it to yourself but measure measure measure - check check check is the only way you'll save time!
I enthusiastically estimated the position of the bend on on the corner of the patch I'm making for the rear left hand corner of the floor pan and got it totally wrong.
In order to turn this negative into a positive I thought I'd share the cock up and say it'll all come good with a bit of heat treatment and then bashing into the shape I should have made in the first place.
What I should have done before I started the corner was make another guide out of masking tape and a bit of tracing=>
Then it is easy to see how far out of position you are (or hopefully not!)
Oh well - cock ups do happen - as I said at the start measure measure measure...