You dint mention about your costume and your hair type and length.
Since it is engagement you will look elegent if you leave your hair free. This hair style will suit neither you have long or short hair nor straight or curly hair. The previous day you can have a trim and blow dry in the parlour. Then on the day of your engagement wash your hair with mild shampoo and give a final rinse with 3 or 4 tablespoons of honey mixed with water or rinse with flat beer (you must keep the beer open for sometime so that it becomes flat). Giving a final rinse with honey or beer will give you immediate glow to your hair, i have tried it many times and the hair remains glowing and shining throughout the day. Once the hair dries comb it well, use hair iron if you have, since you have had a blow dry the previous day your hair might hang straight in that case you just comb your hair throughly. Then take few strands of hair from both the sides of the ears and clip it. Now comb the hair again well and leave it free. You can also hang jasmine flower as much as you think would suit you. Wear a simple but a broad nethichutti. Free hair with nethi chutti and jasmine flower will be looking elegant and beautiful no matter you wear saree or any other costume.