Looking at op and not the thread, sorry guys:
It depends on if the stream is odd or even numbered, aside from that it doesn't matter how long the stream is to determine what finger you stop with. People tend to map odd streams because they use at least a quarter rest note to give time to get to the next set of notes so you're not pressing quarter notes for the whole entire map on certain songs.
So again,
odd: you usually end on the same finger you start with
even: you end on the opposite finger you start with.
Some players use this fact to simply stream at a pace they know is right and don't worry about hearing exact sounds, instead they focus on the sound that signals the end.
Branching off from this statement: I would recommend you focus on every whole note within a stream to give you a sense of pacing, and then from there try to focus on every half note, eventually you can cut that down to focusing on every single note correctly. If you can't even focus on getting every whole note instead focus on what starts the stream and what stops it, and like I said subdivide your focus from there, generally though if you can't even focus or move fast enough to keep a consistent pace to hit even the whole notes it means you're clearly not fast enough and should move to something slightly slower paced.
Your goal should be making the stream sound nice, not worrying about if you're getting 300s or how many notes you have to hit.