Also known asvasant panchamibasant panchmisaraswati puja
A cut or extended corner is corrected without construction by hanging a cloth potli filled with gomti chakra in that corner: white in the North-East, red in the South-East, yellow in the South-West and white in the North-West.
In the cut or extended corner: NE white, SE red, SW yellow, NW white
Mark Om and swastik on the main door, write the name of your isht (chosen deity) and add auspicious symbols such as kalash and darpan. Do it in a good muhurta such as Basant Panchami or after the Sun turns Uttarayan.
Main door
Yes, Basant Panchami is very good for it. Gomti chakra is energised with the same raksha mantra used for yellow mustard, since both are used for protection.