Fantasy is not love
I'm very shy and I have a crush on a woman at church. How do I tell her I love her and want a relationship?
Real love happens when you share a long history with another person. You can only truly love someone if you are in a meaningful relationship.
If you believe you love someone whom you have only seen from a distance, then you are in love with something in your imagination. When you reveal such feelings to a person you don't know, it does alienate them because it makes them feel like an object of your fantasy world, not recognised as a real person.
Your challenge is to stop living in your inner world and to embody your needs, feelings and aspirations in reality. Try to tone down your crush to a more manageable interest and attraction.
Ask questions that show you have a genuine interest in who she is. Get to know this woman, decide if you genuinely like her, and see where that leads.
Being shy can make connecting with other people seem difficult. Work on building your confidence to introduce yourself to people in new social settings. This is key when the stakes are higher and you're introducing yourself to someone to whom you are attracted.
Until you have started to interact with this woman personally, you will not know if you really love her. What you are describing is infatuation - you find her attractive as you watch her from the sidelines.
You will probably alienate her if you declare your wishes upfront. Try to strike up conversation. Invite her out for coffee. Take the time to discover if this is a relationship you mutually want to build.