Inactivity while pregnant

Katelyn • Expecting #2 in September
I'm wondering if anyone else was pretty inactive during pregnancy and had a healthy pregnancy despite this.
I work a desk job from home, so I basically sit on my butt for 8 hours every day except the weekend. I get up, walk into the next room, the end.
After work, I generally cook dinner and do light housework. I'll deep clean the house about once a week.
I don't really go out during the week because my husband works long hours, so by the time he's home it's late.
I live in the south and it's been ungodly hot most of my pregnancy, so although I live beside the park, it's too hot to do much walking. 
Basically my activity consists of me doing light housework, prenatal yoga videos a couple times a week, the exercise I do in my birth class (basically stretching) once a week, and shopping/walking around stores/grocery shopping on the weekends. 
I was walking a few times a week until 18 weeks when it got too hot to continue. 
I'm wondering if inactivity will lead to preeclampsia or something bad. I'll be 31 weeks on Saturday and so far my blood pressure has been good, I passed my GD test, no swelling, and I've gained 18 pounds which doctor says is good because i started with a good bmi. I eat some junk but I also eat lots of protein, veggies, fruits, and whole grains. 
Any insight would be great. I don't want to develop preeclampsia if more exercise could prevent it.