Alternatively, there is a procedure to return an unallowable withdrawal, you would need to contact the HSA bank, it usually needs a special form.
Also note that if you are not maxing out the HSA now, you can do that and still pay your expenses tax free. For example, if your plan is to invest $2500 per year in a single HSA (maximum contribution $3400) you could deposit additional money (up to $3400) and immediately withdraw it and still get the tax benefit. In other words, you get a bill on Monday, put the money in the HSA Tuesday, withdraw it Wednesday, and pay the doctor on Thursday for an instant tax deduction.
