Nic -- You're credit history must be in, "decentish" shape or you would not have been accepted for the mortgage, strengthened by the fact you already have a credit card and contract phones.
You would be advised to keep all your payments by the due date and get a copy of your credit report in 3 months time, to see whether it's in good shape before applying for a loan so close to just taking out your new mortgage.
Try and buy normal household items that you pay cash for in the meantime on your capital one card, then pay it off in full before interest is due or at least the minimum monthly payment if you can't afford.
This will help your credit record to rebuild then apply for the loan when you can see a favourable credit report, by that time the loans position in general could have started to ease off.