I'm not entirely sure about some of the details in your question, since I think you meant to use $10,000 as the value of the futures contract and $3 as the value of the underlying stock. Those numbers would make more sense.
That being said, I can give you a simple example of how to calculate the profit and loss from a leveraged futures contract. For the sake of simplicity, I'll use a well-known futures contract: the E-mini S&P500 contract. Each E-mini is worth $50 times the value of the S&P 500 index and has a tick size of 0.25, so the minimum price change is 0.25 * $50 = $12.50.
Here's an example. Say the current value of the S&P500 is 1,600; the value of each contract is therefore $50 * 1,600 = $80,000. You purchase one contract on margin, with an initial margin requirement1 of 5%, or $4,000. If the S&P 500 index rises to 1,610, the value of your futures contract increases to $50 * 1,610 = $80,500. Once you return the 80,000 - 4,000 = $76,000 that you borrowed as leverage, your profit is 80,500 - 76,000 = $4,500.
Since you used $4,000 of your own funds as an initial margin, your profit, excluding commissions is 4,500 - 4,000 = $500, which is a 500/4000 = 12.5% return. If the index dropped to 1,580, the value of your futures contract decreases to $50 * 1,580 = $79,000. After you return the $76,000 in leverage, you're left with $3,000, or a net loss of (3,000 - 4000)/(4000) = -25%.
The math illustrates why using leverage increases your risk, but also increases your potential for return. Consider the first scenario, in which the index increases to 1,610. If you had forgone using margin and spent $80,000 of your own funds, your profit would be (80,500 - 80,000) / 80000 = .625%. This is smaller than your leveraged profit by a factor of 20, the inverse of the margin requirement (.625% / .05 = 12.5%). In this case, the use of leverage dramatically increased your rate of return.
However, in the case of a decrease, you spent $80,000, but gained $79,000, for a loss of only 1.25%. This is 20 times smaller in magnitude than your negative return when using leverage. By forgoing leverage, you've decreased your opportunity for upside, but also decreased your downside risk.
1) For futures contracts, the margin requirements are set by the exchange, which is CME group, in the case of the E-mini. The 5% in my example is higher than the actual margin requirement, which is currently $3,850 USD per contract, but it keeps the numbers simple. Also note that CME group refers to the initial margin as the performance bond instead.