All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Mere suspicion that the mouse might have urinated in the bag does not make it obligatory to purify it. You are not obliged to purify anything unless you know with certainty that it was stained with impurity.
Moreover, it is only obligatory to purify the bag if you are going to carry it while praying, which is unlikely; otherwise, you are not obliged to purify it, and it is only recommended that you do so. In any case, you must ignore any obsessive doubts, and do not give them any attention at all.
Allah knows best.