that's a common spot..
being that it came out with overspray on it, and I'm guessing you have a fair amount of sandscratches, etc I would suggest letting it dry well, then take some 180 to 220 dry to it.. knock all that overspray off try to sand pretty thoroughly, but the second it goes thru the primer anywhere, move on... once you get a cut to the majority of it, scuff it with a maroon scuff pad to knock any shine down.. blow it off, damp towel/dry towel with paper towels and denatured alcohol... reprime... if it's laying on nice, get a few good heavy coats on...
a suggestion to avoid overspray.. always do your top, horizontal surfaces last... what kinda primer are you using? really shouldn't be having an issue with dry spray, which is really what that is probably, not so much overspray, with a section that small...
when you get a nice prime coat on it, as it dries, look for your minor imperfections, scratches, low spots, etc.. once the primer sets up decent, 8 hrs or so usually, take a rubber squeggie and put glazing putty on the prob areas.. let dry.. wet 220 with a block.. reprime..
now.. on to more tragic beach news....
the rest of the truck... I would STRONGLY suggest you plan a pretty heavy cut whereever there is paint.... really, you wanna be at least to the factory original paint, with maybe a hint here and there of they're yellowish fill primer... you can leave they're bodywork areas if it's holding up, just prime over it...
btw, that blue to the left in your bottom pic, appears to be glazing putty from the prior job...
keep in mind... there comes a point where battling getting a decent featheredge, in minimum areas, becomes not time effective and your better off just stripping it right off the bat... easier to just wail with some 80 on a DA, as opposed to a controlled cut 180..
but if you decide to take the "just strip the last job off" approach, I would just sand the heck out of the truck with some 150 to 180.. it's a good cut for primer to stick to on existing paint, etc...