Registration of the under construction property

I have booked an apartment in Bangalore an year back for 41L+bwssb+parking+ registration+ corpus etc with a reputed builder. I have also got a partial loan sanctioned from SBI for 30L. The project is not completed yet, There are almost 10 blocks in which the builder is saying they will hand over 6 blocks in march end, but it looks like it may take more time. The builders are sending certain dates for registration who wishes to register. We thought we can register before procession since i can get some tax benefits for the year. But here is the hitch - the builders will register only for my UDS . They have given me only one agreement with schedule B for UDS - 18L and Schedule C for construction cost 23L. They are saying that they will register only for UDS since it is under construction site, otherwise they will not give me procession and i have to wait until the other blocks are over and oc is obtained which may take another 2 years according to me. I dont want to under register only my UDS as well as I want to register for the full Property value, Kindly suggest what should i do now.