Sorry Bob, I hate to disagree with you but, the fiberglass stuff out of the can I wouldn't use on the scoop that the OP is talking about. The reason is that if your working with this product over a small area and it's being applied on area that is going to have a lot of vibration...it's just not going to hold for very long. It's fine for putting a coat over top of ground down welds or any place that there is metal holding it in place.
Now...to try and offer a solution...I hate these dilemma's because there are only 2 ways that I can think of to repair this part and have it hold...and I hate doing either of them.
1) Rough up the sides of your scoop, use your mat glass and resin, build up the side a bit so that you can build up the bottom and then cut it to fit your hood. If it could be built up from underneath as well as on the sides, all the better.
2) Use a body panel adhesive or even an SMC adhesive to build up the bottom...I use 3M's 8116 or 8115 a lot, they stick to anything and hold real well, they make faster products with respect to dry time. They are costly, but work and work well. Apply a little adhesive on the sides as well and shape it into the scoop, it feathers quite well. That way you will have the support from the sides as well as the surface that your trying to enlarge.
I hope this helps.