Im so sad

I made soup today for the first time using my new pressure cooker. Chopped up all my vege's, I used Carrot, potato, pumkin, cellery, onion, canned tomatoes, four bean mix, chick peas, butter beans, Soup mix & soup pasta. I used 1 1/2 litres of chicken stock(just coverd the veg).

I used the pressure cooker right, let it boil, and when it started steaming, i let it go for 20mins, then turned it off & released the pressure. As it was releasing I started the smell the burning. I took the lid of when it finished and my poor soup was burnt on the bottom Its edable (sp?) but the burnt taste is all thru it. Its yummy if you ignor the burnt taste lol :P

Does anybody know why this happened? I really want to try it again (its part if my "get skinny" healthy eating plan lol)

TIA