Make a function that makes line segment coordinates centered at point (x y) with slope m

I have a plotting library I'm building source, and want to plot slope lines. I have a function (draw-seg-list device color lst) with the lst arg being a list containing lists with the start and stop cords of a line (x0 y0 x1 y1). I want to make a function (make-slope-seg x y m) that then returns the point list for a line segment centered at (x, y) with slope m.

Example: (make-slope-seg 0 0 0) -> (-.05 0 .05 0) and (make-slope-seg .1 .1 1) -> (.05 .05 .15 .15)

The non-working function I have is:

(define (make-slope-cords x y m)
  (list (- x .05)
        (* y m -1)
        (+ x .05)
        (* y m)))

Which returns the incorrect lines. If I use :

;makes graphics window
(define window (make-graphics-device 'win32))

;plots blue line for function y = x^2 with black axis
(make-plot window 'simple-plot (list "white" "black" "blue" (list (range -1 1 .01) square)))

;makes list of lists containing the slope and x y cords that the slope lines
;are supposed to be centered at
(define cords (map (lambda (s x y)
                     (list s x y))
                   (map (lambda (x) (* 2 x)) (range -1 1 .1))
                   (range -1 1 .1)
                   (map square (range -1 1 .1))))

;plots the line segments generated by mapping make-slope-cords to the coordinate list
(draw-seg-list window "red"
               (map (lambda (lst)
                      (make-slope-cords (car lst) (cadr lst) (caddr lst)))
                    cords))

It outputs the following:

But I want it to output red lines of width .1 (1 square on the grid in the image) with slope being the slope of the blue line(lambda (x) (square x)) at each point spaced by .1 along the x axis.

NOTE: assume that draw-seg-list works. I just need assistance in making the function make-slope-cords produce a the correct list of cordinates