what??

I wouldn't know where to start but I think I would 'let go' bad relationships much earlier rather than being too afraid to face life alone.

For me it's a combination of what mollie and petra said.

It's not your responsibility to fix everyone's problems and or to make them happy, especially at the cost of your own happiness.

Same here nina, I got there in the end on both counts
(not school but further education) but it could all have been much simpler ......!

Same here, Annie. It took me until my late 50s to wake up although my own daughter had been trying to educate me for years.
Also, it's not up to you to fix everyone's problems.

Make more effort at school and follow my dreams.

Be brave enough to go with my heart.

Not to waste time trying to make other people happy but to concentrate on making myself happy first!

I think I would tell myself not to be so trusting

Nope. Like you, I find it impossible to answer. Nothing I could have said to my young self would have made any difference anyway. If, on the other hand, I could go back and actually change myself, give myself some confidence, amongst other things, that would be a very different matter and could have completely changed my future life for the better. Ah, if only!