First, your lower limb is bending more than your upper limb and both are bending too much in the inner limb and not enough in the outer limb. If that's the type of bend you had the first time I can see why it broke. Narrow red oak board bows need to get the whole limb working well depending on how much you're asking of the wood. About the string slipping off, just file your string knocks deeper and it should help. You'd be surprised at how narrow you can make the wood that the string sits on.
