After some research it appears that swelling and pain is unlikely to be testicular cancer. So that's a positive sign.
Swelling is not uncommon from lengthy rides on a bike especially on an uncomfortable ill fitting seat.
It's now Thursday, I first noticed it on Sunday. The pain is reducing day by day. But I haven't noticed any change in the swollen testicle.
I plan to see the Doctor on Monday.
I did a check when I got home and the right one is twice the size of the left one.
I hope it's just swelling and bruising from the exercise bike.