the proverb implies that whatever the circumstances may be one should make the best of them.
i think that you have although grasped the concept , your outline wandered a bit from the topic. for example these two headings are not fully justifying what the topic is about.
Make hay while sunshines( it suggests prudent use of every opportunity while the topic is about using lemons(harsh circumstances) to make lemonade(advantage/gain leverage).

same goes for this second heading..
Lost oppurtunities of youth lead o regrets of old age