Dispatched a sold item but can’t mark it as dispatched!

UK Marketplace seller here. I only sell very occasionally on Amazon so I fear I may be behind the MP times. I received a small order last night and I dispatched it this morning, taking it to my local post office in order to get a printed proof of postage. I used a non-tracked service, which may have been a mistake – because I can’t enter a tracking number as I don’t have one, I can’t mark the order as having been ‘dispatched’. So it looks like I haven’t dispatched it when the truth is that I have! Am I in deep trouble?