There are 2 ways
1. Sine Jaipur is before Ajmer you can deboard the train at Jaipur itself, but you have to show the Ticket to TTE, you must not say to him that you will get down at Jaipur or China.You have paid extra amount upto Ajmer so need not worry, Just get down at Jaipur. If they ask at station and ask you to explain just say them that there was an emergency and make some one or two reasons. Actuall they will not check first, but other instance
2....
more... You can cancel the ticket and book new if you think that you have wasted some money but during this rush period it is difficult to get the confirmed seats. You may try if you like.
I tried this same thing when I was travelling from Coimbatore to Ajmer I have to change the train at Marwar to get another train to reach to Ajmer. But in which train I was travelling was full till Marwar but there was plenty seats available in that train after Jodhpur. The train was upto Bikaner Junction. So I paid Rs.80 extra for Bikaner and deboarded the train at Marwar. There are some logics.