HELP PLEASE BC change

I've been getting my birth control without prescription for over 5 years now. I finally got health insurance and went to see the doc.. he changed my pill to tri-sprintex. now, this new one is 28 days vs. the old one which is 21 days. so, will this affect my cycle? which ones better? is there a risk of getting pregnant with this change of days? (I'm good at taking it every day at the same time). I'm not TTC, but if it happens it happens although I'm trying to avoid it because im not ready yet. if it helps, I'm 23 and healthy.