I had the same issue after installing a Cobb FMIC and big mouth. Fit was tight but one of those two parts caused underbite (did them at the same time, not sure which). I looked at it in sadness for a month and then one day I got the idea to zip tie it using the two squares mentioned earlier. Now it looks perfect, no sagging and that was a year ago. The only issue is the prop rod doesn't lay where it used to but that's not an issue since I have hood struts.
Good luck! Hope that helps.