as you see in the title, i tried doing set imgsprite heading to -45 but it doesnt work. help is appreciated

Figuring out your reciprocal bearing is easy:

- If your original bearing (angle??) is between 0 and 180, add 180
- If your bearing is between 181 and 359, subtract 180.

original heading is 45 then what you want as the 'reverse angle'??? may be 45 + 180 = 225

so your new heading might be a heading of 225 degrees

See

for some ball bounce math.