Today, I apply gelcoat on my bonnet tool and I see almost all of surface look fine, but there is something on the edge of tool as picture 
*polyester gelcoat 400g
butanox 1%
co-bolt 1.5%
mono 4%
Looks like what we call a “gator” (looks like the skin on an alligator). Caused by an incomplete cure of the gel coat which is usually indicative of too thin a layer of gelcoat. However, this is usually seen after applying more material. The second layer attacks the first layer and creates the wrinkling affect. Did you spray gel twice?
Roger, Yes I spray twice !!
But why those appear only the edge of tool ?
Because your gelcoat was thinner there.
It’s possible you didn’t have the first batch mixed up enough before spraying . Applying a second layer over an uncured first can cause that as well as too thin of an application .
http://www.jamestowndistributors.com/userportal/pdfs/GelCoat_Troubleshooting_Guide.pdf
Thank all of you guys so much much