When improvising over standard changes it's important to understand the function of the chords in the progression. You need to see that Gm7-C7-Fmaj7 is a II-V-I progression in F major, and Bm7(b5)-E7-Am7 is a II-V-I in A minor. So if you know how to play over II-V-I progressions in major and minor you can improvise over this song.
Over Gm7-C7 you could simply play F major (which is G dorian / C mixolydian). However, over the V chord jazz musicians often add alterations to add tension that can nicely resolve to the I chord. If you heard the notes correctly (which I don't doubt), then what you heard was a C mixolydian scale with an altered 9, i.e., the note D was altered to add tension. Both possible alterations of the 9 are used: the b9 (Db) and the #9 (D#/Eb). This is very common, and I think it's more natural to view the notes just as a collection of possible notes over a dominant seventh chord that resolves down a perfect fifth. This collection of notes consists of the notes from the mixolydian scale, possibly plus some of the following alterations: b9, #9, #11, b13. You can freely mix notes from the mixolydian scale and altered notes. The altered tensions can also completely replace the standard tensions, which will give you the altered scale:
C Db Eb E F#/Gb Ab Bb.
But anything in between is also possible.
If you want to give a scale name to the collection of notes you found, I would suggest "mixolydian b9/#9", because that's what it is.