Flowers for forgetting a 2 month anniversary is too much. I assume you are young/student, so money isn't that plentiful.
Anniversaries and birthdays are yearly celebrations. And, trust me, as a guy you will forgot one of those as well someday. Exactly once. At that time, you'll have plenty of opportunity to abase yourself & learn how to program your calendar with these dates in advance.
She's childish to not speak to you. A bit of Princess syndrome going on there. You can say you are sorry you forgot (bet you *are* sorry, lol), but you can also let her know that you think monthly anniversaries are a bit much. Ask her how many other couples make this a big deal this often. Say that you would actually prefer small random, unplanned romantic events and yearly celebrations of things like birthdays & anniversaries. Say that she can also do things like this for you.
Good luck. Post what happens, am curious.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh