3 to 12 is a long distance but you have more time than money so you use what you got. The 12k may get you a polished look on your bevel quicker than it gets you to sharp. So even if it looks good you may want to keep going until it is good. It's what you can't see that your trying to fix. Your lower grit stones are leaving microscopic cracks and chips that mid grit stones usually take out. By jumping to a 12k this process will take much longer. If there are no issues with the razor you should be near success.