When you say you failed to add the Dry Malt, did you have it on hand, but forget to add it in time, so you threw the dextrose in later on? For future batches, you can add any malt extract as late as your flameout... a lot of people add malt extract right at the end for various reasons.
How much dextrose did you add? If you had added 1lb, it'll be a tab more dry than the recipe called for, but you probably won't notice a big difference. If you added 3lbs, I would guess it'll dry the beer out quite a bit, and I'd expected that it'll get down further than 1.019.
What do you want to add the candi syrup (or DME) for? If you're looking to use it to carb your beer, they should work, but make sure you use a priming calculator to figure out how much to add.