Completing 3 solutions in a division 4 is likely to lower your score — as a lot of those will only have "relatively simple" problems — and anyone who got 4 correct solutions will have come out ahead of you.

Remember — for you to gain rating points, you need to take them off someone else.

Your penalty of 150 is just the speed at which you completed the problems — in order to not get a penalty you would have to complete all questions within one minute.