If you managed to pray at least one Rakah before the time of Athan of Asr, then you have prayed it on time.

You would be sinful if you had delayed it for no legitimate reason.

If Im unintentionally late for Dhuhr and only have time to start Dhuhr but not finish it before the time and congregation for Asr begins, shall I wait for the congregation and pray Dhuhr behind them.