Christians throughout history have claimed that they are the exclusive religion to worship the only god that exists. Christian apologists claim the religion is the only one that is historically true, logically sound and, further, that everyone must also believe in their religion. However, the facts on the ground show completely the opposite:
Christianity is not historically true
This is proven by the fact that there are no contemporaneous reports of any of the miracles - the virgin birth, the raising of the dead, the feeding of the 5000, and most importantly neither his death, nor his resurrection. In addition, the doctrine that Jesus is the Messiah prophesized by ancient Jewish texts has been in dispute since the beginning, continuing to today, where Jews refuse to concede that Jesus was every the Messiah - specifically for not fulfilling the prophecy of bring peace to the earth.
Christianity is not logically sound
Whatever logical arguments Christian Apologists make, they have had very little effect in convincing every major religion to concede and to follow the Christian God. The reason why is that none of these arguments are meant for acts of persuasion, rather they are there to keep people within the religion - to justify pre-existing beliefs, rather than convincing new ones.
More importantly, it is important to realize that Christianity isn't a single set of beliefs like Judaism or even Islam. Instead, it has split into multiple Churches, and denominations and cults throughout its entire history over matters doctrinal, even to the very nature of the Trinity, their own God! A religion that cannot even agree universally the nature of their own God can hardly call itself logically sound, particularly since all the versions of said God exist to this day - each side unable to convince each other their logically sound arguments are actually true.
Christianity for all
Christianity's insistence on proselytization and evangelism is one of its defining features. Beginning with direct commandments from Jesus himself, that only his religion and only his god and only his special teachings are true and must be spread from a single tribe to all of humanity. Much like the lack of historical confirmation and logical consistency, there is little actual reason as to why Jesus' teachings actually need to followed - it's just a commandment where Jesus co-opted a religion's God for himself, and self-anointed as a deity in his own right! Again, wtih no actual proof.
Conclusion
The above are a few basic reasons why Christians cannot claim to be a true religion. Thoughts?