Will i be able to travel to USA?

i am british citizen which means i do not need a visa to enter USA, however i do need to fill in an ESTA form. it asks about convictions or if you have ever been arrested. i was arrested and cautioned over two years ago for possesion of a very small amount of cocaine, will this affect my chances of going to USA? they say they only refuse 0.5% of people, it was only a caution and i was only 18 at the time, stupid and Naive! I have never been in trouble before or since. will i still get in?