How can i use (modulo x y) function to create loop

does anyone know how i can write a function for big-bang which basically loops an animation.for my task i have an animation of a car which currently goes from left to right but ends when it touches the right hand side,however,i want it to repeat itself so it continuesly goes left to right back to left and right non-stop.this is the excerise description

Exercise 45. Design a “virtual cat” world program that continuously moves the cat from left to right. Let’s call it cat-prog and let’s assume it consumes the starting position of the cat. Furthermore, make the cat move three pixels per clock tick. Whenever the cat disappears on the right, it reappears on the left. You may wish to read up on the modulo function.

; WorldState - Image
; places the cat into the BACKGROUND scene,
; according to the given world state
;when the cat dissapears on the right it reappears on the left
(define (render cw)

[(> cw (+ width (/ (image-width CAT) 2))) (place-image CAT cw X-CAT background)]
[else (modulo (round width (/ (image-width CAT) 2)))]))

i had to use the round function as modulo returned an error stating it wasn't an integer is there a way i can format this.and even then it didn't work

(main 13)
round: expects only 1 argument, but found 2