I kinda did something simillar with my first build not knowing how the stock heatsink should be installed. Well i installed it correctly but due to my newbiness i thought it should be oriented in a special way (it was an AMD down blowing HSF ofc it didn't have a certain orientation....doh).
Anyways, what you need to look after is if the thermal compound spread too much and it got on the sides of the CPU. Usually you should clean the off, and reaply TIM when reaseating the HSF to ensure that there are no pockets of air (air is a thermal insulator and prevents heat transfer) and to ensure that the middle of the chip (the the actual chip is located under the integrated heat sink) has connection with the heat sink above.
That said, if you don't have any spare TIM at the moment and if the TIM didn't spread on the sides of the CPU after you repositioned the heat sink you could test the CPU. A normal power on self test won't stress the CPU that much anyway. I feagure it should still work even if the TIM isn't perfectly spread in the middle, but in the future you should wipe the CPU and heat sink clean and reapply TIM. I recommend using Arctic MX 4 - it's dielectric (doesn't conduct current so you won't fry the CPU, mobo if it accidentally gets on sensitive parts) and doesn't require curing time. Plus it's guaranted to last 8 years...
nVidia video drivers FAIL, click for more infoDisclaimer: All answers and suggestions are provided by an enthusiastic amateur and are therefore without warranty either explicit or implicit. Basically you use my suggestions at your own risk.