I mailed my I-751 application last April 15, 2013 (certified mail) to California Service Center and they received it April 18, 2013. My GC will expire on May 06, 2013. I'm really concerned now because I'm not getting any letter from them, not even the receipt notice. I mailed it within the 90 days, is there any chance they might deny my application? Thanks! I really ne ed you help.