notifying a school of your intent to matriculate

So far I've sent in a written letter with my deposit.

 

No additional notification of "intent to matriculate" is required. Once you accept the offer of acceptance and paid the deposit you have indicated your intention to matriculate. This doesn't change EXCEPT:
1. You notify them otherwise or
2. They withdraw or rescind your acceptance (for whatever reason) or
3. They catch you holding on to other acceptances after May 15.

 

I would be a good idea to call and be sure that your 'intent to matriculate' letter arrived at the admissions office. Also confirm that they cashed the check (a better form of proof). There is a horror story on this forum about the admissions office not receiving a sent letter and check and rescinding their offer.