What should one do if one feels he does not belong to/ in a church/ group in the church? Should one keep volunteering/ serving?
This is a great question, one which will be very useful for others too.
I used to go to a Hillsong affiliated "church".
I always felt like an outsider. In fact, 'they' make you feel like an outsider especially if you do not tithe. If you do tithe, especially if you have just started, they make you feel welcome and accepted in a way that they would never do if you do not tithe.
It boils down to manipulation and spiritual abuse.
I was put under pressure to begin tithing by the 'elders' of the church as well as the pastor himself.
Rather than just do what somebody else says I should do, I conducted an in-depth study on tithing and realised that what they were teaching (tithing being a requirement for modern Christians) is absolutely incorrect.
The next time I was 'talked to' about tithing, I presented the 'elder' with a three page Word document which summarised my study.
They shut up and went away with my document.
About 3 weeks later I was asked to not share the document with anybody else in the 'church', and asked if I could please find another church to attend.
The reason I have shared this story is because it almost certainly isn't you that is the problem.
As others have said in this thread, church's can be awkward places to navigate socially.