All the advice you been given so far is good, It happened too me when I first introduced my girlfriend too tickling (cuz she found it hard at first too react too it because it was a sensation she was not use too) but I did not let it question my confident I just kept trying each week. And as she got use too it and more comfortable and relaxed with it all and how it works it allowed her too become more at ease with it and therefore she laughs a lot now and even occasionally screams XD (not out or horror lol)
I just kept trying different things, till I learned all about her tickle sweet spots, pressure too apply, tools that work the best for each spot and of course setting the mood etc etc
And in the end all the hard worked paid off for me and it even helped me to learn new things about myself and my girlfriend learned a thing or two about herself aswell i also feel this experience has helped too improve my tickling skills, also now she enjoys the tickling and it even courses her too get turned on by it. So it just shows. Just keep at it, don't lose confidents and have some patients and it will get better mate, and in the end will be worth it