These should fit your car as I believe the required offset for a Polo is between 32mm and 38mm, so 37mm, so these should fit with no probs and fill the arches quite nicely.
Be careful when buying wheels that are not the correct offset for your car, it is always best to try the wheels on the car before you buy if you can. If the wheels you are looking at are a wider offset than is specified for your car. This means they will stick out more than they should and could possibly rub on the wheel arch. On the flip side if you were to fit wheels with a narrower (is that actually a word?) offset, the rims or tyres could foul the suspension or the inner wing. but with a narrower offset you could fit spacers (although I wouldn't recommend these) to compensate and make the wheels sit further out.
Here is a little diagram to explain offset and backspace.
