Laying on back during third trimester?

So I was wanting to get eyelashes extensions at 34 weeks for my maternity shoot. The woman doing them mentioned it takes a couple hours and I might get uncomfortable laying on my back that long. I remember reading that doctors say to avoid sleeping on your back during the second and third trimester because it makes the uterus press on the vena cava. My question is, do you think it would be okay to lay on my back for a couple hours or should I just avoid it all together? I'm not against getting false lashes for myself if I can't get extensions. 🙂