Hello!
I am sorry that nobody has gotten back to you in a timely matter :c
For future reference I believe on the plant shop page it does tally up how many flowers you have turned in! Perhaps it counts them up AFTER the complete 150 for milestones. So you'll just have to remember to add 150 to what your total is!
But other than that only top 50 show on the leaderboard!
I hope this information will be helpful to you!