You probably have to retrain your left hand technique as far as how you play.
It may not be a stretch so much as bringing your thumb further into the back of the middle of the neck so that your palm and fingers are elevated a little more.
Then when you do the --3--5-- part, don't stretch so much as do a very fast lift off 3, rock your hand quickly while doing a slight thumb mute on the E string, and then quickly play the next note.

You could also exercise your fingers by doing the Vulcan peace sign a lot but I wouldn't do it in public.