How do I log/count these calories?

So I'm going to be making what I call my "rainbow dinner" tonight. It's cherry tomatoes (red), peppers (orange), crookneck squash (yellow), zucchini (green), red onion (purple), and mushrooms (white) stuck on to skewers and grilled. I also will be grilling some chicken thighs. I will be brushing it all with a roasted red pepper dressing (50 cal for 32g/2 tbsp) as it grills. I go though about 8 -12 tbsp. I haven't made it since logging, so I won't have an accurate amount that I use till I measure it out tonight.

QUESTION: How do I calculate how much of this dressing I'm actually getting? I just brush it on, I'm not actually marinating it. A lot ends up dripping off into the grill, I'm not sure how much it soaks in and how it will change the weight of the veggies.

Am I being too anal retentive? Should I just wing it with a guesstimate? Am I over thinking it? Everything else has been pretty straight forward so far. I just don't want to be WAY off if I record 50 calories instead off 200 or something.

Then again, one meal of uncertainty won't kill me. It's not like I am eating 1000 thinking I only ate 400 or something.