There's still 9 days until fuku ends so it's not impossible, try doing everything you can to get coupons like lucky wheel, convoys, plunders, activity packs, ninja puzzles, group summons, rewards for collecting ninjas and events f.e myoboku trial

even leveling up your ninjas in home screen can gives you coupons (every 5 levels i think)

Aside from what are already stated above you can try checking the Ninja handbook bro.Try digging some treasures and maybe you can find seal scrolls. Sacrifice some sun scroll too if you think doing so will give you enough seals for coupons. The more you recruit the better the chances of getting coupons. Before recruiting tho you must estimate first if you are gonna make it or not. If not then better let go of fuku and wait until those ninjas are drawn from treasures for instant 4 star.

based on your wordings I assume you still haven't touch any of your coupons. If so then that is good.

Word of advice to all f2ps out there, every coupon counts. If you miss 50, 20, 10cps etc goodbye fuku it is. Before spending make sure you have enough for the whole process.

Hope you make it bro. Goodluck! :)