"till now" and "so far"
The two phrases overlap in meaning, but they also have a different usage.
"until now" (more natural than "till now" in my opinion) is more general in meaning. You can use it for pretty much anything that happened in your life. For example, you might say "I've never thought about it that way until now", "I've never tasted this kind of food until now".
"so far" seems more specific and purposeful. It works better with something you started at some point with a purpose. So if you've joined a new company, you might say "So far, things are going well at work". With your new boyfriend, "So far, so good", etc.
Your sentence "Till now, I've practised 3 times" is also specific to whatever you're practicing. So "so far" is better in my opinion.