No need at all. There is no embarrassment in using dialect phrases from wherever. However, on this course we do not cover dialects in any real depth, just a few simple variations that are widely understood across all of Wales.
If you happen to pronounce dych chi as /dach chi/, /dech chi/, /ych chi/, /ŷch chi/, /dych chi/ or whatever, nobody reasonable is going to care very much. If they do care, just find somebody more interesting to chat to!
If you are not living or working in Wales, just stick with whatever the Welsh Plus pronunciation videos on Youtube use. If you do live or work here, then you will pick up the local pronunciation etc pretty quickly anyway. The whole 'north' vs 'south' thing is a great over-simplification of the actual variation in the five-ish main dialects and many more, more local differences.