I realise this is the benefit of hindsight, but it is generally wise to wait until the very last day to submit your witness statement, if you have not received the other side's.
There's often a fair bit of leeway given in small claims as many judges recognise that litigants in person are less likely to be au fait with procedure. You're still within the deadline for submissions, so you could just submit a supplementary statement clarifying your position and see what happens.
You were sensible in your wording insofar as you said you didn't recall receiving a notice, which is different to alleging that you definitely did not. That said, it would be wise to try and submit something to clarify your position, now it has become apparent that not only was a notice issued, you also responded to it by way of an appeal.