I don't think you're going to be able to achieve your expectations with that battery pack and motor combination.
According to the Dynomometer results, the HSB 48V 1000W motor would be drawing around 25 Amps at 45 km/h
(363 rpm on a 26 x 2.00" tyre).
That 11.5Ah pack would only be able to supply 25 Amps continually for approximately 0.44hr before it was fully exhausted, which would give a range of less than 20km on a level route.
I estimate that you would need at least 14.5Ah capacity to complete a 25km trip at 45km/h without pedalling on a perfectly flat route without any stopping/starting and no headwinds.
Riding at full throttle without pedalling will reduce the range considerably, so you would need to restrict your maximum current and/or ride at a slower more efficient speed in order to obtain a longer range with that particular battery pack.
Alan