Gaps. You are going to have some regardless of how well you install your kitchen!
How to do it yourself
While silicone and caulk are the go to fillers in most situations, sometimes using a timber quad moulding (pictured above) is a great solution for larger gaps or if your caulking skills are a little shaky.
Timber moulding can be purchased at Bunnings in a variety of sizes and even profiles if you’re after something more decorative. Cut it to fit, paint it to match your walls, and fix it into position. You'll be more than amazed!
DIY level - Beginner