Does it matter what hand you use?
When signing, it does not matter if you sign as left-hand or right-hand dominant. The biggest thing to remember is to pick which hand you want to use as the dominant hand and stick with it. You should not switch back and forth between dominant hands. Most signers will be able to understand your signs no matter which hand you use as the dominant hand.
I am actually left-handed but choose to use my right hand as the more dominant hand simply because most people are right handed and it eases understanding for them when first learning to sign.