Cover or tint a vertical line on front tooth

I want to cover or tint a thin vertical line on a front tooth. Any suggestions on what product I should use? I tried using this one:
https://www.net32.com/ec/primedent-flowable-composite-a2-4-syringe-vlc-d-78088
I used a uv light to harden and it looked great but fell right off. Thanks for any info.

 

Maybe you could post a photograph of the tooth?

 

You have to etch, bond before using the flowable composite...

 

As Kim points out, this is not something you could do at home. Not that's it's particularly dangerous, but it simply isn't designed for home use. Covering crack lines is not necessary for strength, simply for appearances. They nearly always have to be slightly drilled out about 1mm so that the final composite is flush with the existing surface. And you have to have polishing tools.