First advice is that if 13:50 on last Sunday was really pushing yourself, don't do 13:50 on your next long run. If that feels like a maximum (near race) pace, that's not something you want to do in training regularly. So be comfortable doing 15-16-17-18 min/miles in training. It will not prevent you from going sub-16 on race day if you go an appropriate 17 min/mile in training. Whereas, going 13:50, when it's an inappropriate pace in training, could lead you to be unable to do sub-16 on race day because of all the fatigue/damage you've built up in training and a lack of true adaptation to the training itself. Ultimately, I think you'll be fine as long as you've been putting in some training recently. Even if the 7 miler was a race level effort, Daniels calculator still says your HM pace is around a 14:30 min/mile (3:10 HM finish). And if this was a race level effort, then your long run pace should probably be around 16-18 min/mile anyways per Galloway and Daniels calculators.
Secondly, your sole goal is to avoid being swept. So keep that in mind in all of your race day decisions and think of all the ways to aid in that happening. Think about sacrificing some sleep in order to be on the first bus and be able to line up as one of the first people in your corral/starting group. This will give you a maximal buffer from the balloon ladies as possible. Think carefully about your hydration strategy and how to keep yourself from having to use the restroom on course. That'll likely cost you minutes compared to a slightly slower pace. Then on race day, I'd plan to do a 16 min/mile run pace from the outset. Get some practice in these last few weeks as to what a 16 min/mile pace feels like. I'd suggest keeping the ratio (if you do run/walk) the same as you currently do (like keep 60/30 if that's what you're doing), but just aim to slow your running pace down such that the average ends up at 16 min/mile pace. See if you can find a "comfortable" running pace (during the run/walk interval) that gets you to a 16 min/mile. If not, then consider changing up the ratio a bit to make it happen. The slower you go on race day, the easier it'll be to avoid being swept and maintain the same pace throughout the race. The faster you go from a 16 min/mile the more buffer you'll build from the balloon ladies, but it also increases the risk of "blowing up" and ending up going far far slower than a 16 min/mile average. If you can't maintain a 16 min/mile pace from the outset to the last sweep point, then there likely wasn't a different pacing strategy that would have gotten you there.
All of this advice is what I'd normally give, but I'll add an extra consideration since you're pregnant and any advice I may give should be double checked with a professional.
and good for you that you’re doing all three! Every year, my mouse hovers over the challenge for a second, but the thought of getting up early TWO days in a row on vacation quickly kills that idea 
