As a Christian and worship leader at my church, I’m shocked at what you’re planning to do. I’m equally surprised at the many replies giving you tips on how to go about it, but very glad a few others eventually explained it correctly.
I don't think it's a matter of what is "correct" but merely a matter of what the expectations typically are within churches. A lot of churches want their musicians to be bona fide participants in the life of the church (which implies agreement with doctrines, values, etc.). On the other hand, I have known churches that see it as a form of discipleship or even "friendship evangelism" to fairly quickly allow/invite newcomers to join into ministries, including the worship band (if they can cut the mustard musically). It's less common (perhaps because it means extending trust), but it does occur. Additionally, my observation has been that the more in need of musicians a church is, the more open they are to inviting anyone to play who has a modicum of ability, with less regard to things like "calling" or church membership.
To the OP: Like with many things, relationships can make a significant difference. If you have (or make) friends who are worship musicians and/or do some networking, there is a higher possibility of being asked to sit in with a worship band. I think it's pretty cool that you want to play worship music and I'd love to hear more about what's drawn you in that direction.