They probably know what your answer is though if everything else is crossed off. People checking answers usually use a different colored pen, particularly red, so as to indicate what the corrected work is and avoid any confusion. Whether or not they'll cross out what they believe to be a wrong answer depends on whether or not you'll see the actual test with the mistakes (which is unlikely) or whether you'll just receive your grade. If you're just going to get your grade for results, then there probably wouldn't be much trouble over it.
The best thing to do is always put a box around your answer, or some other indication. With a lot of numbers and scribbling, it can sometimes be difficult for people checking the answer to determine what your answer is.
I think you're good.
