confused by clothing sizing

beckstyle

Hi ladies, I will be a first time mom soon and I am having a hard time with baby clothing sizing! I got a lot of great baby clothes from my two SILs but I don't get the sizing. Some is newborn, some 0-3 months, some 3 months, some 6months. I know it really goes more by weight and brands are different. I'm worried I won't have enough newborn sizes. Is it bad to put a newborn in clothing that's a little too big? Thanks!