Talk to someone who works there.
I work at Curves and no machines should hurt you, ever.
If you have an existing weakness or health problems, you should discuss this with the staff and they can advise you which machines you should skip, or perhaps give you alternate or modified instructions.
Ask for someone to watch you as you do the circuit. You may be using the machines with improper form, straining your joint- knees and backs are the two most vulnerable places that tend to get strained when this happens.
Also, you should be going to Curves 3 times a week on nonconsecutive days, not 5 times a week. For optimum results from strength training your body needs 24 hours to restore muscle chemistry to proper levels. On non strength training days, you may walk, jog, swim etc. If you insist on going to Curves those 2 other days, you should work stronger on the recovery boards, and do harder moves on those, rather than the machines. (On strength training, or regular Curves days you should be doing the "sprint" as Gary calls it on the machines and giving your all on them, and just using the recovery boards for RECOVERY.) Curves staff should be able to teach you in person moves you can use on alternating days. PM me if you want more info.
Actually Curves is the opposite of one-size-fits all. I have been to many gyms, including expensive ones and the machines are not adjustable for different sizes. Curves has several pads and forms that you can use based on your height to make machines fit you properly. If your Curves does not provide the pads and forms, please speak to the owner about this problem. There are also modifications you can make (example- standing closer for petites or further away for talls on the lateral lift) to get the most out of your workout.
Curves is EXTREMELY healthy! We have a bulletin board filled with women who have lost 30, 40, 50, up to 90 lbs at our Curves! I just read an articel in Looking Good, with a woman who lost 169 lbs just going to Curves and following their diet plan. I currently follow the Curves exercise plan and diet plan and I have lost 27 lbs over the past year. I gained a few back on the
Disney Cruise and started back up and I'm down 10.5 lbs since this new start. It absolutely works and I am thankful I've found it. I was Curves member for 2 years before I was asked to work there part time evenings (after my other job, I'm a teacher by day) and I have found it very rewarding to help others reach their weigh, health, and exercise goals.
Some more tips I can offer is to stretch BEFORE and AFTER you work out. If you're not doing this, that could explain the problems.
As far as quitting, you state you've signed the contract for the year. Have you completed one full year? If you have there is no penalty. If you have not then you are trying to get out of the contract you signed and you will have to pay a fee- again, talk to the owner. But give it a fair try before you quit. I wouldn't want you to miss out on all the great rewards you can get from following this wonderful program.
I am in clothes that are 1-2 sizes smaller and I am still going down. The diet has helped me, too, because diet and exercise really go hand in hand- they work much better if you do both. 
New studies have shown that jumping up and down, not continually, of course, 15 minutes a day is actually wonderful to strenthen leg and hip bones if you are heading towards osteoporosis. I do agree that if you have any really serious medical conditions, it is probably not the best place for you. But it works for me and the constant changing keeps me from getting bored so I actually keep going. Unlike my 7 previous gym memberships that lasted a month or so.
