回复：forgot to submit I-94 when

don't worry about it! it is not a big problem if you come back the US with 30days. because of your I-94 can not be reached INS via Flight Company or say INS can not find out your I-94 during a long time after I-94 collected.
when you come back you just surrender your previous I-94 to Flight Company is ok. better put your marks(explanation) on it.

I was the trublemaker several years ago, but I did entry USA with success, and still stay here.

Good luck!