Is it permissible to pray Maghrib with the ablution that I intended only for Asr prayer, given that the time for Maghrib has entered and I am still in a state of ablution?

It is permissible for you to pray Maghrib with the ablution (wudu') with which you specifically intended to pray Asr, even if you performed other prayers with it; this is based on the madhhab of the majority of scholars, and it is the preponderant opinion.