Rhythm Game Note Scaling

I am programming a rhythm game in C++ using SFML and OpenGL. I am currently working on implementing a type of hold note (the length of the note is variable) where the size of the note scales based on both the predetermined length (ex. 2 seconds) as well as a user defined "speed" (where speed defaults to the song's bpm and can be adjusted from there). I am able to properly scale the sprite to on the interior of two other sprites that would outline the start and end position, but I need it to be extended to fit the full length. I then have an issue where the note needs to be adjusted back half of the