[Solcielo lawrencia]

I assume this is a tree stump look you're going for. I think what you did was successful. However, I think an actual stump would look better because the base looks like a bunch of branches clumped together. This might not be a problem if you have lots of plants and rocks covering up the base.

As for soaking it in hot water, I don't know what the melting point of fishing line is so I can't offer suggestions other than to put in some test pieces of fishing line in boiling water to see if it softens or melts.

 

[Solcielo lawrencia]

You boil until the water stays clear. You'll have to do several changes of water and this will take several hours minimum.