KCL sign and negative result
The way I wrote my KCL equations had the current of the branch shown flowing into node Vds. By passive sign convention the current has to flow from + to - on the resistor, so the negative sign pointed to the fact that I reversed this.

I think the key is to be mindful of what each term in a KCL equation represents (current) and if a - sign shows up, track it back to the corresponding current. In my case, the question asked for the voltage with this polarity, meaning that I needed to reverse my sign.