The coin looks OK to me at first sight, but I am no expert. Wait for others to react.
If you doubt the authenticity of a coin, don't buy through eBay. They are particularly unhelpful. Their bottom line has way more priority than stopping fraud. If your doubts are slight, it is best to ask for the weight of the coin. If you get no answer, an evasive answer or a weight that is too high, don't buy. If the weight is too low, consider wear and shroff marks and decide on the risk you are running.
Since you already bought the coin, it is best to await delivery, weigh it yourself immediately. Also, inspect the edge (the third dimension). If you see a seam running horizontally or another metal in the centre, your coin is a fake. Run over to a friendly jewellery shop and ask them if it looks like good silver.
If it turns out to be a fake, lose no time. If you paid by paisepal or paypal and you can still block payment, do so. File a complete complaint against the seller at once. Don't bother with feedback yet. There is no deadline, but there are deadlines for complaints, returns etc. Make sure you respect them, or they will be used against you in full force and with a sigh of relief.
Peter