I had a similar experience. Before I was a casual flyer, and then on my way to Wenzhou in an Airbus A320 we had a sudden jolt of turbulence going sideways. After that experience I didn't enjoy flying, and would grab the seat armrests at any form of turbulence.

It sounds daft, but I used to repeat a phrase in my head when flying: "safe, calm, happy". It's more of a psychological trick than anything else, but I found it helped me to adjust my thinking at moments.

Recently, I took a role which meant working abroad, and then I realised that I would need to be doing quite a lot of flying to get back for various events. In July I've flown 9 times, 2 of which were on a propeller plane (Bombardier Q400). The experience of doing that many flights means that I don't experience any anxiety when flying, but I still tend to strap myself in a bit more tightly whenever there's some turbulence.

Oh, and the other thing that helps is sitting next in the window seat - being able to look out the window when the plane is taking off, in flight and landing helps. You also get to see some great views.