I am sorry to heard that. Don't worry and keep calm, Just try to blink your eyes as fast as you can that will cause tears in your eyes to flush out the chalk dust. Then, you shall use clean water to flush your eyes as soon as possible. You may feel burning and foreign feelings in your eyes. It should be temporarily. It will be Ok after you flush your eyes. If you still feel burning eyes or eye pain etc for a long time, you'd better see a eye doctor.
Blink your eyes fast until you get tears to come out of your eyes, then the tears will wash the chalk dust out and you will be ok. Also, you can rinse your eyes with cold water to wash it out promptly. However, you know, the main components of chalk dust are calcium carbonate and calcium oxide, which are liable to dissolve in water and produce alkalinity materials; if the alkalinity materials are too many, they will stimulate the ocular mucous membrane in some serious case, resulting in the damage to the mucous membrane, furthermore leading to chronic inflammation, even the decrease of vision. You should consult an eye doctor as early as possible and ask him to prescribe some antibiotic eye drops for you if you feel worse. Wish you feel better soon.