Is it considered a Bid'ah (innovation) to determine the Qibla direction for prayer inside a prayer room (musalla) that is not oriented towards it, knowing the necessity of facing it for the prayer to be valid, and given that some people use the noble verse as evidence: "And to Allah belong the east and the west. So wherever you [might] turn, there is the Face of Allah. Indeed, Allah is all-Encompassing and Knowing"?

If the worshippers deviate from the Qibla in such a way that they are not facing its direction, then their prayer is undoubtedly invalid. However, if the deviation is slight, such that it can still be said that they are facing the direction of the Kaaba, then their prayer is valid according to the preponderant opinion. It is better to face the exact Kaaba to avoid dispute.

Adjusting the direction of the Qibla for the congregants is a good thing, and it is either obligatory or recommended. As for some objecting with the verse "So wherever you turn, there is the Face of Allah," this is a mistake on their part. The verse is either abrogated by the command to face the Qibla, or it refers to praying on a riding animal during travel, or where the Qibla is hidden, or turning one's face for supplication. No scholar says that the verse means that facing the Qibla in prayer is not necessary.

Your action is correct, and there is no cause for objection against you.