Fury Viper

I bought 2 mainland parcels and joined them, they are water parcels. when i try to terraform and bring the land up, only a small strip at the back will actually come up, the rest stays sloped. i am pretty familiar with terraforming and how to edit the whole parcel to terraform, i just dont get why it will only raise a small part. even when i lower all of it or flatten all of it, it still is sloped. any help is appreciated.