@Mehak_Bhargava
Yes. Logstash still using its default pipeline "main". your configuration in pipeline.yml didn't take effect.
Please restart logstash service while running above tail command and look for lines similar to the following,
[2020-01-09T07:59:06,000][DEBUG][logstash.config.source.multilocal] Reading pipeline configurations from YAML {:location=>"/etc/logstash/pipelines.yml"}
[2020-01-09T07:59:06,106][DEBUG][logstash.config.source.local.configpathloader] Reading config file {:config_file=>"/etc/logstash/conf.d/beats/beats.conf"}
[2020-01-09T07:59:06,133][DEBUG][logstash.config.source.local.configpathloader] Reading config file {:config_file=>"/etc/logstash/conf.d/syslog/syslog.conf"}
It will tell you where it's reading pipeline config from and what are the conf files applied.