issue a legal notice demanding the builder to complete and hand over the possession of the flat, together with delay compensation as was agreed by him in the agreement to build, if he does not oblige or comply with the demand made, then you can file a consumer complaint before the district consumer court seeking for delay compensation, if you seek cancellation of the flat then you will have to file the complaint before the Karnataka State Consumer Disputes Redressal commission, at Bangalore seeking cancellation and refund together with interest @ 18% p.a plus compensation and damages till refund is made by the builder.
If you approach builder and seek cancellation 15% of the total cost of the flat can be demanded from you by the builder.
It is better to take the first remedy than choose the 2nd remedy.