Given this paragraph about muscle strains and that my symptoms include severe and acute pain with movement limitations, how bad is my strain?

A strain can occur as a result of improper body mechanics with any activity (e.g., contact sports, lifting heavy objects) that can induce mechanical trauma or injury. Generally, the muscle or tendon overstretches and is placed under more physical stress than it can withstand.[1] Strains commonly result in a partial or complete tear of a tendon or muscle, or they can be severe in the form of a complete tendon rupture. Strains most commonly occur in the foot, leg, or back.[3] Acute strains are more closely associated with recent mechanical trauma or injury. Chronic strains typically result from repetitive movement of the muscles and tendons over a long period of time.[1]

Degrees of Injury (as classified by the American College of Sports Medicine):[4]

First degree (mildest) – little tissue tearing; mild tenderness; pain with full range of motion.
Second degree – torn muscle or tendon tissues; painful, limited motion; possibly some swelling or depression at the spot of the injury.
Third degree (most severe) – limited or no movement; severe acute pain, though sometimes painless straight after the initial injury

You likely have a Grade 3 strain, often considered amongst the most severe types