Surely this happens a lot though, if I check my oil level that would be a fair indicator (I've only recently changed it)
Pull the dip stick and smell the end of it, and the opening; any fuel fumes?
Mine didn’t smell of fuel by the way. The oil and fuel will separate over time. Any dilution of the oil cannot be a good thing. I would just drain it and refill with new. An oil change is cheaper than an engine rebuild.