Help with basic front roll?

Hello I've recently started attending a ju jutsu class and on my second day our Sensei had a more experienced student teach me rolling. I understand I'm supposed to keep one knee down and my weight primarily on the knee that's up. I tuck my arm beneath my body and my chin against my chest. Then push forward with my bent knee.... but I usually hurt my shoulder or my knee will smack on the ground and then my the roll becomes stupid and I end up rolling with my side. I make sure my foot and knee are pointing forward too in an effort to not go sideways but it happens anyways. What frustrates me is that after the first day doing such a basic thing I can't get it down. It's been two days since then and I've been recording myself to see what the problem is but I don't get it.