First of all, stop blaming yourself. Improving your diet will improve the situation, but what you ate might not have been the cause of the pre-diabetes. There is a lot said about diabetes which comes under the heading of "blame the victim", and it really isn't helpful. It could be hereditary, or there could be other causes - there are people in your situation who have perfectly healthy lifestyles.
If you haven't been given any advice, there are two websites you might like to look at. One is the official one which will probably be recommended to you at some point - that is
https://www.diabetes.org.uk/
The other is not official, but I have found it more helpful. BUT THIS IS JUST MY OPINION, AND I AM NOT A QUALIFIED PROFESSIONAL, SO FEEL FREE TO IGNORE.
https://www.diabetes.co.uk/ The forum on this site has a lot of interesting information, some of it conflicting, so use a bit of common sense when reading the posts.
ANOTHER PERSONAL VIEW COMING UP! I have found it helpful to reduce carbohydrates more strictly than official guidelines suggest. I still have fruit, but in very reduced amounts, and never ever have fruit juices. You need to do your research and decide what is right for you.