Maternity shoot question

So I ordered this beautiful dress on etsy and I got it. It's absolutely amazing I love how it look but there's one little problem...there's no lining so my belly and everything below is see through. I wanted to get my shoot done in a the park but now there's no way I'm going out showing my underwear. Do you guys have any suggestions on what I could wear underneath so my underwear don't show? Or should I just get it done in the studio even though that's not what I wanted