Freeze/anxiety response on top

My experience on top is limited, and when my man asked me to get on top I got really stiff and anxious, and asked him if he could guide me through it. The one time I’ve had a successful time was when a dude guided me for a couple seconds and let me go, or when I was drunk and not at all nervous. This only happened twice, and I feel like my biggest issue is lack of guidance and general insecurity? Is it appropriate for me to need help as it is something I’m warming up to? Is it a turn off that I can’t just do it on command? Should I give up on being on top? I feel like it could be fun if I had more practice and security in it, but I feel like the person/atmosphere is rarely right for me to get outside of my comfort zone for it. I don’t want my partner to feel like it’s more trouble than it’s worth because I want to do something that he wants and is pleasurable for him too.