Modifying an Existing BRD file to a bigger outline Software won't let me maintain Copper Pours

Hello Everyone,

I am fairly a beginner with Cadence and have ran into a problem that I haven't figured out yet and I am hoping that someone here can lead me on the right path. I started this job by modifying an existing board as shown below. I have created a new schematic and used the board below as an input file to generate my netlist, It might not be very legible but the outline for this board is 15 inches x 0.58 inches, so far so good.

It might not be very legible but the outline for this board is 15 inches x 0.58 inches. Here is a more zoomed in image:

Now , I need to turn this into an 18 inch board so I am going to delete the left side edge of the outline and and extend the length by 3 inches, so far so good.

The 2 smaller rectangles with vias are just for thermal purposes and the vias reach out to the opposite side with a similar coppor pour on the other end. Now , since I extended the length of the outline to 18 inches, I need to extend those copper pour heat sinks as well, after I tried it , here is what happened:

It only created that small piece on the left and I cannot go past that ( seemes like that's the 15inch limit of the older outline) despite extending the outline to 18 inches.

I would like to get some tips on that. Now I haven't laid out any components which will be somewhere in the middle ( where the bigger coppoer pour rectangle is right now). I will have to delete that one before laying out the components, Even thought I did not get to that point yet , I would love to get some tips as well on how to recreate it with the components laid down and have it extended to the edge of the new outline (just short of 18inches).

Thank you all very much.

Neil Mustafa.