Hi, and welcome!
I am just going through the body alignment stage, and having the same challenges. I think the cost of the kit is very good, and perhaps a third of the price of most others, so you have to bear in mind that it also has some fitting issues. It will not fit right straight out of the box. It will need some work to get it to fit to your bulkhead/chassis/frame combination.
The advantage is that fibreglass is not a huge issue to modify and as Mulberry and DaveCymru have said, there are different ways of tackling the bonnet gap. Some build out the bulkhead and some add length to the bonnet. Either is fine and whatever works for you.
One thing to consider is some strengthening "webs" on the inside of the bonnet - Gary has added these to a car he was building and the big advantage with them is that is will help the bonnet keep the right shape, particularly down the sides where the catches are mounted.
Heres the picture:
