When you are worrying and cannot stop, your mind is mastering you. But no one worries continuously. Worry comes in waves. So when you are worried, sit as usual, take some deep breaths, go around the body for steadiness and observe what is happening. Try to isolate the first image that comes in; and hold it as long as possible. Then, after you have lost yourself in thought and recovered from it, back-track if you can.
You will have to work harder at remaining conscious or present. The waves carrying the worrying thoughts will be very strong. You are likely to be doing a lot of huffing and puffing as the mind rebels; it wants to quit trying to be conscious and get on with the worry unimpeded. But you should now have the control to keep separating from the thought-line, pulling back to yourself - even though you soon end up identifying with the worry again.
To remember to separate is the thing. There is the worry, which is the thoughts; and there is you, the observer. You are not the same.
What counts is the number of times each minute, hour or day that you remember to separate; not how long you may think you hold each separation.
Do not get disheartened. It is difficult. But while you continue, even though you seem to fail so often, you are winning - gaining in consciousness.