Here is what I normally do ...
http://https://www.fiatforum.com/members-motors/340090-my-sisley-panda-4x4-division-north-18.html?p=4059784
http://https://www.fiatforum.com/members-motors/340090-my-sisley-panda-4x4-division-north-18.html?p=4059784
One more from a better angle
Is that a pipe bender you are using there?
Tip here don't cut the floor back so far grind back the vertical part of the floor bend say 11 o'clock until the edge of the inner sill can be grabbed by mole grips then pull the inner and floor pan together weld along that length repeat stretch grip and repeat the wonky edge should then be ground straight then re welded. Until a good joint is created Then use some 1 mm or 1.5 mm sheet create the vertical section. To be then rejoined to the sill edge