Accidentally put oil/gas mix in lawnmower...now what?

I did it this morning on accident and the mower worked fine for 2 hours of mowing. This evening I went to finish mowing and the mower worked ok then just stopped. I tried to restart it and it works for a second then stops. I checked the levels and put just plain gas in and it still won't stay running. The oil is a little low. Do you think that could be the problem or did I really mess it up by puttin goil and gas mixture in this morning?