i guess it should not make a problem as on your I-20 on the 3rd page, it does mention till when your opt ends, i mean the end date of the opt period. It is not worth of applying again to USCIS becasue you gotta pay 380$ and it does take almost the same time  of the time which take you to get your opt card in the begining. I had went to Nepal 6 months ago on opt but i had misplaced my opt at the time i departed for Nepal. But, i had bought the tickets and had already taken off from work to go to nepal, so i travelled nepal and I had applied for the replacement for my opt as I would need that on my way back to USA at the immigration. Luckily, I had found my opt card when I was on the way to Nepal. But even after i got back from Nepal, my opt card that i had applied for replacement was still on the process..... .
Bottom line is, you should not have a problem and the other thing is that, it shows on your sevis the duration of ur opt.