As the admit cards have been made available yesterday,  there might be huge traffic to the website. With lakhs of students trying to download their admit cards, it is quite common for a server slow down. So give it a day or 2 before you try to download your admit card. Or try during late midnight when the traffic is comparatively lesser or during early in the mornings. Few Students who tried that option were able to download their admit cards. It is unlikely that your application would have been rejected.