A 10w-30 oil is 10 weight when cold and has the viscosity of a 30 weight oil when hot. That 5 cold weight and 10 hot weight difference is no big thing. Now, if you had put 20w-50 oil in you might have a problem, but even then it probably wouldn't immediately hurt anything to just run it. It just wouldn't flow as well on cold start-ups.At cold temperatures, the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up, the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C, the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot.