should i worry or not

Few days ago,I had mentioned about sending my I-751 packet to USCIS Vermont Service Center which I really did last Monday.I sent it thru priority mail via USPS and paid an extra amount so that i can have the tracking number and what not just in case.Well,yesterday when my husband and I were both in the vehicle,I asked him if he had seen the receipt I put in there.As quick and hurry,he answered,"I threw it away I thought it was trash".Yea,he threw away the tracking number that i got from USPS.Now,I don't know how to trace it though my husband suggested of calling them today.I just hope that they can tell me whats up with my mail now (crossed fingers) and hopefully I'll be at ease while waiting for a receipt from USCIS.