I'm gonna assume this is your first 'run' with insulin? How long have you been going at it so far? With the hypo feeling, if you're starting to get dizzy midway in the gym or on the verge of blacking out and etc, don't bother calculating how many carbs to take in and so on at that point in time. Save your life first. As Godzilla said, you'd want to start eating quick carbs - simple sugars or you could get some glucose tabs from a pharmacy as those work faster. If this happens on a regular basis, you'd be able to start gauging how much carbs you take in to stop the hypo and slowly taper down from there. It's always better to overshoot your carbs when going hypo because you can potentially die.

If you've not had any experience with insulin, you'd ideally want someone to guide you - both plan out a proper insulin protocol for you (dosage, time between meals, hypo precautions, etc) and walk you through execution. Insulin is a very powerful hormone and can put on serious muscle on you if used right, but the keywords here being 'used right' so you'd want proper guidance.