Firstly, I can tell you straight off that when you begin meditating for the first time you will find it almost impossible. Everyone does. It's not really about whether you can meditate or not, it's about whether you can begin the training of becoming a meditator.
So perhaps the question should not be 'What if I can not meditate?'. Perhaps the question should be 'How can I develop the skills to meditate?'.
Meditation is about mindfulness, it is about being able to focus the mind, control your thoughts and become aware of every moment that you are alive. Meditation is about giving yourself the space to reflect, to be still, and to find a deep calm.
The first thing to do is to forget about whether you can or can not do something. That's just the mind giving you a bunch of fearful feelings of failure and ineptitude. Take action to get over that and get yourself a timer. Set it for 1 min and then sit still and just let yourself be.
Become present in the moment.
Become aware of your breathing.
Sit and just allow whatever thoughts come into your head to simply drift by without any big reaction from you. Watch them and allow them to float away if possible.
When the timer goes off ease yourself back into the world, stand up and carry on with the day. That was the start of your meditation practice.
Often it can still be a struggle just to get 1 min of awareness and mindfulness so I'm going to give you three really powerful focusing exercises that you can work on at any time through the day. These can help you to sharpen your mind, and improve your concentration and focus.
With these skills, you will find your awareness increasing, and as a result meditation will become a more natural process for you.
These are all visualization exercises and can really help to sharpen the mind.
1. Close your eyes and visualize a single digit number.
Picture it however you want in the forefront of your mind. Now add a second digit, and then a third. Keep going with this until you reach the limits of the number of digits that you can hold in your imagination.
When you have reached the limit keep this figure at the forefront of your mind, your inner eye, for 2 min flat.
2. Close your eyes and picture a fountain pen slowly writing your name on a blank piece of paper.
Keep picturing the pen writing your name slowly over and over until the sheet is full.
3. Close your eyes and visualize a simple colored shape. For instance a golden triangle, a red circle, a blue six pointed star. You can stick to one particular shape or you can imagine a series of shapes drifting in front of your inner eye.
You can even use these exercises as your meditation for a while, plenty of people use objects such as candles or deities for this exact purpose. The point is not the exercise or the technique, the point is to be free of fragmented thoughts and attention and to raise your own strong awareness and mindfulness.