You can always quit, especially if you're not 100 percent sure. There is nothing wrong in backing out, there is nothing wrong in reversing your decision. Because at the end of the day... it is our happiness that matters and not the happiness of other people.
If a saleslady assisted you so many times and she is expecting you that you are going to buy an item from their store... if you are not so sure that you want the shoe or shirt that you are trying... don't buy it. Never buy it because you feel so sorry for the saleslady, never buy it because the saleslady is getting angry. Only buy it if you are 100 percent sure that you like it, never buy it just to look nice or you are trying to please someone else. It is yourself that you should prioritize and not other people.
Just like saying yes to someone who ask for your help... if there is a sudden change in your life and you needed more your time and money... then quit, make an excuse and never try to apologize. Because you can always say no without feeling bad. Any decision that will make your life bad is bad. Remind yourself that you can always quit if you are not 100 percent sure, there is nothing wrong in turning down someone's expectations, you don't owe them anything so don't feel sorry if you didn't give them what they want.
You know in yourself if you are sure about something, you know in yourself if your decision is right or wrong. Because at the end of the day... the goal in life is to minimize regrets and never feel bad with the decisions that you made. So if you still have the chance to turn down something for the sake of your own good... do it, do it before it's too late.