How do I correct this impulse angle calculation?

I am using the sprite origin as x1 and y1

I then swipe down from sprite, either down to the right or left, then let go. On touch end when I let go I record x2 and y2.

I then apply impulse - angle(x1,y1,x2,y2)

When x2 is less than x1 (swiping down to the left) it works fine and shoots the sprite up to the right.

If I swipe down to the right and x2 ends up greater than x1, then the sprite fires off down to the right in opposite direction I wanted.

Please advise if my angle setting is wrong and what formula I should be using to calculate the angle.

Thanks for any replies.

See this demo:

dropbox.com/s/ayiha83qgv0tu5j/SwipeImpulse.c3p

Thank you