As any Doctor Who fan can tell you, there is a limiter in time travel. It's called the "Blinovitch Limitation Effect".
The 1972 Doctor Who story "Day of the Daleks" revealed that one cannot go back in time again to change something that one failed to change the first time.
That is basically the sci-fi version of the very real "Maple Leafs Limitation Effect", which was discovered in mid 1968. In that case a certain sorry hockey team cannot go back to the NHL payoffs and win a Stanley Cup, no matter how many times they try.