2 usual causes of pulling it inside, when you normally do hit your target, are dropping the bowling shoulder as you go into the release and not doing a deliberate, full pushaway, resulting in early timing (ball/hand getting to the release point before the feet get there).
Usual solutions are to keep shoulders square and think that in practice sessions, and, also in practice sessions, to make the pushaway a very deliberate and purposeful one to almost force your timing back to normal. I say, "in practice sessions", because during normal bowling, this might throw off your concentration about regular items like targeting, lining up, following the transition, etc.
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"We get old too fast, and too late, smart."
