Can I sue CrossFit or my gym?

Even without a waiver, you cannot sue them for injuries that are normal or reasonable or foreseeable consequences of this type of activity (e.g. overuse injuries, spraining or straining something, stress fractures) or which are due to your own fault (e.g. overexerting yourself when you were not in shape to work out so aggressively). The law bases liability, or the obligation to pay compensation, in personal injury cases on fault, or doing something intentionally wrongful or at least unreasonably careless (negligent). If you were injured because a trainer had you do a dangerous action, or because of faulty or unsafe equipment, you may be able to sue; but if again, you suffered just the sort of activities that come as a normal risk to this type of training, there is no compensation. 
To give an example: I practice karate. One of the styles I practiced used a ball of foot (toes pulled back) kick and practiced a lot on kicking pads and heavy bags. My toes were not flexible; I could not pull them back enough, and years of kicking things with my toes caused bad osteoarthritis in my right big toe. I can't sue my dojo becasuse a repetitive use injury or osteoarthritis is a normal risk of choosing to engage in this type of activity; the dojo and my sensei did nothing wrong and are liable.
In your case, if CrossFit was at fault, you can sue for 1) any medical costs not paid by your insurance; 2) lost wages, if any; and 3) and if you have suffered significant long-lasting disability or life impairment, some amount for "pain and suffering."