Yes, Jesus was a jew and his earliest disciples were jews.
So, you gonna be a jew too?
Or are you simply lost in the time warp?
Actually Jesus and his followers made a significant break with the Jewish religion of the time. Like Christianity today, Judaism had come to rely more upon it's own traditions rather than scripture:
Mar 7:9 And he said unto them, Full well ye reject the commandment of God, that ye may keep your own tradition.
There are many more examples. The Jewish hierarchy of the day rejected Christ and persecuted his followers. Paul says:
1Co 15:9 For I am the least of the apostles, that am not meet to be called an apostle, because I persecuted the church of God
Gal 1:13 For ye have heard of my conversation in time past in the Jews' religion, how that beyond measure I persecuted the church of God, and wasted it
Today's Jews are descendent's of those Jews who persecuted the church of God.
Observing God's holy days has nothing to do with being Jewish.