For some reason, the mySprite struct moves 2 times faster in the left direction (a key) than the right direction (d key), despite the magnitudes of delta_time and speed_x being the exact same when either of the keys is pressed. When this code is run, the logs tell me for a key: -2 and for for d key: 1. How is this possible?

typedef struct
{
    int width;
    int height;
    int x, y;
    pixel *pixels;
    bool *mask;
} sprite_t;

sprite_t mySprite;

void update()
{
    // Clear the surface
    SDL_FillRect(surface, NULL, SDL_MapRGBA(surface->format, 0, 0, 0, 255));

    Uint32 *framebuffer = (Uint32 *)surface->pixels;

    // Draws pixels to the frame buffer
    for (int i = 0; i < mySprite.height; ++i)
    {
        for (int j = 0; j < mySprite.width; ++j)
        {
            int pixel_index = (i * mySprite.width + j);
            setPixel(framebuffer, mySprite.x + j, mySprite.y + i, rgbaToUint32(&mySprite.pixels[pixel_index]));
        }
    }

    // Reset speed before processing input
    speed_x = 0;
    speed_y = 0;

    if (key_state.w)
    {
        speed_y = -(SPEED);
    }
    if (key_state.s)
    {
        speed_y = SPEED;
    }
    if (key_state.a)
    {
        speed_x = -(SPEED);
    }
    if (key_state.d)
    {
        speed_x = SPEED;
    }

    // Halts execution of update until the frame rate reaches target time
    int time_to_wait = FRAME_TARGET_TIME - (SDL_GetTicks() - last_frame_time);

    if (time_to_wait > 0 && time_to_wait <= FRAME_TARGET_TIME)
    {
        SDL_Delay(time_to_wait);
    }

    // Finds difference between last and current frame and divides by 1000 to convert to sec
    float delta_time = 0.016f;

    last_frame_time = SDL_GetTicks();

    int old_pos = mySprite.x;

    // Update sprite position
    mySprite.x += speed_x * delta_time;
    mySprite.y += speed_y * delta_time;

    if (key_state.a)
    {
        printf("for a key: %i n", mySprite.x - old_pos);
    }
    if (key_state.d)
    {
        printf("for d key: %i n", mySprite.x - old_pos);
    }
}

Tried adding logs to isolate the problem.

They should print:
for a key: -1
for d key: 1