Birth control help??

So I signed up for a monthly birth control type of thing that will send me bc when I need it. I’m 17 but never been on birth control just because it was a hassle before I could get a prescription online. Anyway, my cycle used to be bad (40-60 days) but recently had been normal for a while but right now I’m on day 3 of my period after 56 days between. I know most birth control says to take it on the first day of your period when you are first starting it, but I don’t want to wait another two months for a period to take it. Should I just take it now or wait until my next period? :( also, since I’m still technically in puberty, do you think my body will change? Right now I feel like I’m shaped like a refrigerator and I’m hoping that will change. 😂