Congrats to you on your graduation .

Congrats to you on your graduation .
This morning,I attended my teacher graduation ceremony, then at lunch I took her out to eat a cream. I dare(d) her that if she eat (ate) ten cream, I will (would) pay the bill. Then (When) she had eaten 10 cream(s), I had eaten 7 cream(s). So now I'm sick in my stomach (I feel sick/ I have a stomach ache). I just sent her a message to ask how about her feel (she felt), she answer(rd) that she feed bad,too.

congrats is ok in a casual situation, but a more formal situation would need the word in full - 'congratulations'.

also talking about 'a cream' doesn't make sense in English - you could say ice cream or cream cake. :)