If you do not know cars much, do not do it yourself like coolant change or flush. This is because that there are things that must be done correctly such as bleeding air in engine, otherwise, you may get engine trouble, even explosion. Coolant replacement and flush are different from cars to cars.
There should not have problem now because you just added 200ml into coolant system (8-10L capability). But it is better to flush it ASAP.
Go to a garage, it costs $50 or 60 for replacement and $100 or a little more for a flush.