your back isnt use to the position u had it in. in a few days it will get better. if u can stand it try to do some cardio. jumping jacks, cardio kicks, running in place.. something that will get your muscles warmed up and u sweat..then try to stretch it out. ly on the floor on your back. arms stretched out at the sides on the ground. cross your right leg over your body and put your knee down... keep your shoulders on the ground. your back will come off the floor some.. hold that position for about 30 secs and repeat. when u do this breathe thru it dont hold your breath..u may have to adjust your body to get your knee to the ground and keep your shoulders down. repeat on the other side. hold for at least 30secs.. that should pull out the muscles that got tight..make sure u r warmed up though. dont do this with cold muscles. u will feel the muscles start to relax so repeat this until u r comfortable with it.