What would happen if u add poer to contact lenses?

So I have ol contacts and am bout to oder new ones now I have -2.50 vision for them how ever I feel ii got a litte blinder and I caint make appointment with local eye clinic because I mess up when I renew my insurance and forgot to ad eye care and you know ho over price they chage you when u don't have any insurance ...well what who happen if I bump the ower a litle to -2.75 wich is the next one?