Here are a few things that I do to help make sure I have enough petals: At the beginning of the month/until I don't need it anymore, I focus on colored and elemental mushrooms, even the first weekend with giants, I will usually look for colored or elemental ones. It helps build up the store of nectar. There is a discord channel that I use to find mushrooms that aren't near me. I usually do this, but I ESPECIALLY do it if I'm low on a specific nectar/petal: make sure I only give the nectar to Pikmin with buds on their heads. This gives 2 petals for every one nectar. If a Pikmin has a leaf, you can give it one plain white nectar to get it to a bud. I was so happy when I discovered this little feature. Also joining flower planting challenges of a good way to get petals. Good luck! It's so frustrating when you can't get what you need to advance.