Flaring old steel lines on the car is a challenge with the tool you have which looks like a rental set and which may have been used several times ...Here are some pointers

1. Practice on a piece of scrap steel tubing if you can (as you have been)
2. Scrap off any coating on the steel line first.
3. Use a wrench or a screwdriver sideways to get extra leverage to crank the wing nuts down as hard as you can get them.