You're fine. I also just had a mid 50's approved. The DU is picking up your score, which is a huge plus. Other things that DU likes is money in the bank or reserves, like 401k's or your 4K. Payment shock is also in the DU algorithm. If you are putting more than the 3.5%, even better. DU loves loans w/ 5% down or more. It won't show in the automated underwriting, but your wife returning to work will tip any doubt in your favor, seeing you are qualifying on only one income.
Find another problem to worry about.
EDITED TO ADD: Some lenders have requirements not to go over 45%. We call this an overlay. Ask Dollar point blank if they have any ratio overlays on DU. If they do, you need to make some choices, like moving your loan to someone that underwrites to the DU. Your appraisal is portable. I suspect Dollar delivers to many of the same investors we do, and they will have a home for your high back ratio. Given real estate is no longer the guaranteed asset it once was, I agree, money in the bank has far more value these days.