BellaOnline Forums Hobbies and Crafts Crochet How do you modify a pattern?

Hi all - newbie here! Looking for help modifying this pattern from moda dea website:
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Personally i would work out the size i want it to be.Then because that pattern is made over a number of rows to make it longer you could repeat the pattern until you have completed the fan/shell(or motif) shape of it and if you wanted it still longer you could do a scalloped edge if you don't need it quite so long again.To make it wider you want to work out over how many chains you need to make one pattern(shell/fan). From there you add that many chain to the foundation chain. Then i would have a go and if it doesn't work i frog it and start again.

thanks - I figured that's what I have to do- I was hoping it would be easier like a formula or something...oh well!

my question to you is have you tested your stitching gauge?
I have found that I tend to stitch bigger if I use a bigger hook and that will increase your length and width also.