At the last step of rewind(triple or nothing) two sting lands on my middle finger and one string lands on my pointer. So I can’t dismount.
http://yoyoexpert.com/learn/035-advanced-rewind.html
Practice is my best advice. Don’t worry, you will get it. I promise. 
Nothing should land on your middle finger. This is all centered around your pointer fingers. Also, if you’re catching the yo-yo on two strings, try using a thinner yo-yo.