collision struggles

Ball::Ball(const Vec2 & pos_in, const Vec2 & vel_in)
{
    pos = pos_in;
    vel = vel_in;
}

void Ball::Draw(Graphics& gfx) const
{
    SpriteCodex::DrawBall(pos,gfx);
}

void Ball::Update(float dt)
{
    pos += vel * dt;
}

bool Ball::Colliding(const RectF & walls)
{
    bool collided = false;
    const RectF rect = GetRect();
    if (rect.left  < walls.left)
    {
        pos.x += walls.left - rect.left;
        ReboundX();
        collided = true;
    }

    else if (rect.right > walls.right)
    {
        pos.x -= rect.right - walls.right;
        ReboundX();
        collided = true;
    }

    if (rect.top < walls.top)
    {
        pos.y += walls.top - rect.top;
        ReboundY();
        collided = true;
    }

    else if (rect.bottom > walls.bottom)
    {
        pos.y -= rect.bottom - walls.bottom;
        ReboundY();
        collided = true;
    }
    return collided;
}

void Ball::ReboundX()
{
    vel.x = -vel.x;
}

void Ball::ReboundY()
{
    vel.y = -vel.y;
}

RectF Ball::GetRect() const
{
    return RectF::FromCenter(pos, radius, radius);
}