with a long arm- sid is quite difficult- how straight of a line can you draw with a pair of handle bars 12"+ above what you are drawing on?
that's why many long arm quilters charge alot more if asked to do sid. your quilt will probably look fine-
once it is washed/dried...very few people unless at a show/being judged- look at the quilting with a magnifying glass.
if you were in my area i would invite you in to try some sid with the long arm to see just what it is like. I tell people when they bring me their quilt- i am not real good at free motion straight lines...patterns are easier. i always have samples to show people so they can decide if they really want sid & are willing to pay the extra for it.