You said something that doesn't seem right to me. It was "until I get in shape..."
Look around your class. If you're in a typical adult class, you'll have many classmates who would not look flattering in unitards or whatever. Most are in class to get into shape.
The real answer to your question is that you have to feel comfortable and able to move in any type of dancewear, be it a unitard or sweats.
If it's easier for you to move in class in a unitard, regardless of how you look in it, go for it. If you rather wear sweats, do that.
When I got older I was embarassed that I had lost all the tone in my chest. I used to wear baggy t-shirts, which I tucked up and under my elastic belt (my pelvis and legs still look good). But then I realized I was having problems with my body center, and the baggy t-shirts covered up my ability to see my full body in the mirror. I stripped down to just a unitard, and could see my full body in the mirror and take corrections.
A dancer needs to be comfortable and functional. Comfortable in the physical sense. The body is the focus of dance, and we all have different bodies. We have to get over any "inhibitions" about how we look so we can dance.
balletboy[/i]