Am I obligated to complete a good deed that someone else started and I became too lazy to finish, and am I sinful if I do not complete it?

If the polls and surveys bring benefit, and you have pledged to your friend to help with them, then fulfilling a promise is an important moral virtue, and breaking a promise is a trait of hypocrisy. If your breaking of the promise was merely due to laziness, then you have sinned, and you must repent. But if it was due to its difficulty and your inability, then there is no blame upon you, and you must make up for what you can and apologize to your friend for what you are unable to accomplish.