Signs of when your about to hit the friend zone?

Hit the friend zone yesterday after i left asking this girl i liked on a date too late, the date was great and i had a lot of fun and built up a lot of attraction but it just didn't feel right for the both of us.

I did all the Cat String Theory and a lot of other powerful attraction techniques but it just didn't avoid the friend zone, i knew this would be difficult in the first place as she's in my social group and i suppose i see her quite a lot, so maybe that had some impact on the friend zone.

But in the end we came to a mutual agreement that it wasn't feeling "right" right now and that maybe something could happen in the future because we both still like each other.

Any who, There isn't really a forum on this so any tips on how to know when your approaching the friend zone?

Thanks.