can I add gum arabic to my fondant to make gum paste?

No, that will give you modelling paste which is fine for figures but not for making flowers.

The one from Nicholas Lodge will give good results.

http://www.firstimpressionsmolds.com/sugarpastefondantgumpasteandpastillage.aspx

Scroll down a bit.

that's what I am afraid of.. thank you!

To make a gum paste-like product, you need to add gum tex, tylose, or cmc to you fondant--NOT gum arabic.

If you're using Wilton fondant, you add about 1/2 tsp per lb. If using a softer fondant like Satin Ice or FondX, add 1 tsp./lb.

If using Duff's fondant/Fondarific or ChocoPan, you cannot make it into "gum paste" by adding any gums, as it's chocolate based & won't dry hard.

Rae