I don't think there will be a problem, but keep careful track of the temp and don't warm the tank up too fast. I'm not totally sure on this so make sure to get a second opinion.
Some people prefer to use 2 smaller heaters rather than one with a high wattage.
Their reasoning is that if one stops working, the other will keep the temperature from dropping too quickly. On the other hand, if the thermostat on a heater sticks and it doesn't shut off, the other will stop going on and if the wattage on the defective heater is low, it will not be able to overheat the tank.