I appreciate you taking the time to duplicate the steps you've been taught, and to describe the effects - please take care of yourself!
You're not required to do a longer exhale, if I'm being really honest - the goal is to extend the length of your inhales (and not even necessarily breathing deeply, just regularly and more smoothly).
Speaking partly from research and partly from personal experience, you can experiment a bit and see what helps you best. Some inhale-hold-exhale patterns that I've seen helping people are 7-5-4 (i.e. seven seconds inhale, five seconds hold, four seconds exhale), or 4-5-4, or similar ratios.
Personally, sometimes doing a long exhale as a start is often more helpful, because it's a good way to trick the brain, but any method works so long as you're slowly increasing how long it takes you to inhale (this is the main part of it). However long that takes you to accomplish, that's how long it takes.
If it hurts to immediately do a large inhale, then uh. Don't do that? You don't have to? If someone's telling you to, they might be more concerned with following their education than looking at the person in front of them.
One thing I would say is that you don't have to correspondingly increase how long you hold your breath with how long it takes you to inhale. A rhythm of, for example, 2-1-3 can be good to start off with, but only if you find it helpful.
Additionally, sometimes squeezing something in time with your breathing will be a better assist than counting - can be your own shirt, or pants, or someone's hand, anything at all that encourages your brain to focus on something other than your breathing (this is one of the reasons why yoga is so popular). Stress balls, fidgeting toys, necklaces, etc, are also helpful but sometimes completely overlooked by people like therapists.