It's not too late to add the missing sugar. Just boil it in a small amount of water, but be sure not to burn it.
You'll want to use just a few ounces of water to avoid diluting the beer (or over filling the bottle?), so boiling on a stove will be tricky.
To get the absolute minimum amount of water, you could try dissolving and sanitizing the sugar in a ...
Basically, you don't need to worry about it. I add coffee beans without any sanitation at all. I've even added unsanitized mushrooms right out of the woods without problem. By the time you add that stuff, there's not only alcohol n the beer, but it has a low pH. Those two things combine to make it very resistant to infection.
Carbonation level has a significant influence on mouth-feel. You could try carbonating it up a bit further, maybe to 2.8 or 3.0 volumes of CO2. Obviously this isn't going to "fix" everything. This is a simple thing to try and is relatively easy to un-do (in a keg).
But you could probably should just leave it as-is.
We did an experiment about this at www.experimentalbrew.com for our Experimental Brewing podcast. Here is a link to the experiment parameters and results....https://www.experimentalbrew.com/experiments/hop-whirlpool-does-steeping-lower-temperature-improve-final-hop-character
For a double IPA, I suggest a moderate-to-high bitterness and a massive hop flavor, with ABV in the 7.5-10% range.
Denny is right-- You can really play with those hop additions and find your own groove. Remember, the later the addition, the more flavor in the final product.
Given your specific hop requirements, here's what I would do for a 60 minute boil. ...
If you'd like to simplify your batch and increase the hop flavor and aroma, I'd make the following recommendations: Use just Simcoe for your bittering. It's likely you won't notice much of a difference in using or two types of hops since all of the aroma and hop flavor will boil off, leaving you with just bitterness. For your flavor hops, move them ...