Thank you David for your reply. I tried by turning off the snaps and after selecting the dimension with mouse click (arc line), filled 20' in the box. Same issue remains for the arc
Then I filled the 20' setback under preferences> edit behavior> concentric > jump, thinking that I would not have to change anything on the arc and will rather change the straight edges on the sides by filling out the dimension boxes. This time too as the change occurred on sides the setback got distorted at the arc
When I first chose concentric>jump for 20', it comes out fine all sides including the arc. It is when I change the dimensions (by filling the box) either on the arc or any sides, that the arc setback gets distorted.