Seems like you had a tough time. You did good though! Judging by the results so far, I'd say you're good to move on to the next lesson, while keeping in mind a few things:

Leaves and Branches are well executed. If you're having any trouble with drawing contours on the leaf's/petal's surface, look up reference and study those. Make sure you're giving yourself enough room and have the page in a comfortable position when drawing branches as a few tend to go in and out very slightly. Arrows are great, dont be afraid to make em a bit bigger as theyre coming toward you and overlap more. (if you need examples, check the arrow page again)

There's not as many mistakes on the plants as you may think. Give yourself time to experiment and find out how to tackle each part of the plant, some of the more complex plants may take more thought but its better to have a plan than no plan. You can always refer to the demos and lesson pages for some ideas too.

Cast shadows are tricky on cacti and mushrooms, try and focus on shapes and dark places, not using lines to draw the light parts. The mushroom demo is a great example of this. Speaking of those, make sure to put a cap on your plants as well, you dont want them floating above ground.

As mentioned before with the plans, don't skip construction, on leaves or extra mushroom cap bits, and so on. Draw your leaf, and add onto it, just like the complex leaf example, pitcher plant, or this review https://drawabox.com/lesson/3/8/plantconstruction You want to first follow your flow line, and then add the extra parts.

Work on some more plants when you can, especially complex leaves/petals, or any that deviate from the normal to use additive methods, use dots or something like that to measure the propotion of them if they end up too short or big, and you'd be good to go! If you want to challenge yourself a bit after thats all done, you can try adding some detail too, but thats up to you.

Good luck on lesson 4, always try to seek some assistance if youre confused, and keep at it! It was a lot of work but in the end it got you past the hill, you're ready to climb the next.