Need advice-postponing Step 1 until after 3rd yr starts?

hi--i am only 5 days away from test day and i desperately need your advice. i am really not prepared to take it. i feel like i studied all wrong for this test and tried to learn too much in too much detail and haven't gotten through everything yet. i am so mad at myself for being inefficient and i am scared i am going to fail. i tried to push back my test date a week but all the spots were filled up. i start 3rd yr in 2 wks and am really tempted to push it back 3 or 4 wks and take it during 3rd yr. is this a crazy idea? is it ever done? any advice would be great. thanks.