There's a tab inside the build menu called Claim, and it'll have tools for expanding and shaping your claim in it! Took me a while before I found it too. Just be aware that the larger the claim, the more resources your totem needs for upkeep. If you need more claimable tiles, make sure that you grab the area 300 node in the research tab from your claim menu. :>
#Claim Expansion
upbeat stream