Personally, I would return them and buy a pair that fit properly and make you look great at the weight you are today

You'll feel good in the new jeans and perhaps that will give you the confidence to keep going.
I used to feel the same way and would squeeze into smaller sizes, creating a muffin-top. Buying the next size made me look so much thinner so I stopped worrying about the size and just got what looked good

Perhaps the small jeans would motivate you, but I think they'd just depress me since it'd be another pair of jeans I couldn't wear.