This is a huge subject. But the answer is that the scale changes with each chord. There is not a single scale that works for an entire song (unless the whole song is one chord). But nobody just plays scales in a good solo. Scales are just a framework on which to build a solo. If good solos were just a bunch of scales, improvisation would be really easy, and all good classical players would also be good improvisers. But they are not.
Here's a list of what scales "fit" which chords. But a good solo will have approach notes, enclosures, etc. that aren't even in the chord or scale.
https://www.jazzbooks.com/mm5/download/FREE-scale-syllabus.pdf
The big band arrangement of Blues in Hoss Flat that I'm familiar with is not in Bb, but in concert Db. It's hard to tell from your avatar, but looks like you play tenor, in which case, that's the key of Eb. If it's a standard blues, the changes are Eb7 Ab7 Eb7 Eb7 Ab7 Ab7 Eb7 Eb7 Bb7 Ab7 Eb7 Bb7. Yes, you could get by with parts of the Eb blues or F pentatonic scale on much of it. But that would be a very boring solo with many nasty note clashes on certain chords. Say you play an Eb minor pentatonic on the first chord and land on Db. If you're still playing that Db when the chord changes to Ab7, you're on the 4th, which is going to sound terrible unless you resolve it to something in Ab.
On September, I assume the solo is on the chorus. In your key (Bb), the chords are probably G- C7 A- D- repeated a few times with an Ebmaj7/F on the last one. Similar story as the other song. You play your G minor pentatonic, land on F, then clash big time on the C7 (4th again).
I would take a voice leading approach, meaning smoothly transition from the guide tones (3rd and 7th) of on chord to the same guide tones on the next. For September, you could play a G minor line, emphasizing the Bb or F, then either remain on the Bb when you change to C7 or transition from F to E. Then continue on playing something in C mixolydian. It's these transitions to the guide tones that makes a solo sound melodic and outlines the chord changes. Somebody should be able to listen to your solo entirely unaccompanied and still "hear" the chord changes.
From your other posts, sounds like you play by ear mostly. You should stick with that until you learn some music theory. I imagine the whole purpose of this class is to teach you what I've outlined above.
EDIT: I found the original Blues in Hoss Flat which is actually in Db and revised my post to match. But your class could be playing an easier arrangement in a different key. So don't use the chords I posted ver batim unless you know they match your arrangement.