8" not real big LOL ..trust me that is big ..No Kits are going to help you .. you need much more than a kit..
White is not just white .. white has a thousands of shades.. your white could have yellows, reds, more grey than white .. you can buy white gelcoat buy its self cheaper than in a kit .. but your 8inch place when fixed properly will be an area about 16" by the time you sand 4inches around the area..
Your way over your head here dude .. you can do it but you need to research this carefully b4 you try this on your own. And if someone hit you make them pay to have it fixed .. you could easily have a 800 - 1200 dollar repair job there
Take the boat to a fiberglass repair shop and get some estimates. and make the other guy fix
This is true^^^
We had about a 5 inch long piece on the bottom and the guy had to go back 2 feet. That was 400 but probaly should have been 600 the way the guy talked that fixed it.