What does 'half the size of my pinky nail' mean? Compared to the entire 8mg, how many mg would you say it is? Bupe is only a partial agonist, so the CNS depressant effects are not quite as strong as typical full agonist opioids like oxycodone, heroin, methadone, etc.. So for instance if you took roughly half an 8mg subutex, I do not think you will 'overdose'. If you have no tolerance, it is quite possible you will get higher than you would like and experience the negative effects of opiates, such as nausea, vomiting, sweating, dizzyness, etc.. But the chances of you experiencing an overdose to the point where you need medical attention is small. Though there is still a chance, none of us on here will be able to definitely tell you whether or not you need to go to the hospital..
THe best thing we can tell you is to monitor your breathing, and have someone you trust come watch you in case you pass out and cant be woken, so they can call 911.