WASHINGTON/SAN FRANCISCO—The ransomware gang accused of crippling the leading U.S. fuel pipeline operator said on Monday that it never meant to create havoc, an unusual statement that experts saw as a sign the cybercriminals’ scheme had gone awry. The FBI accused the group that calls itself DarkSide of a digital extortion attempt that prompted Colonial Pipeline to shut down its network, potentially causing extraordinary disruption as gasoline deliveries dry up. In a statement on Monday, Colonial said it expected to “substantially” restore operational service by the end of the week. The terse news release posted to DarkSide’s website early on Monday did not directly mention Colonial Pipeline but, under the heading “About the latest news,”  it noted that “our goal is to make money, and not creating problems for society.” The statement did not say how much money the hackers were seeking. Colonial Pipeline did not offer any comment on …