when you say the steel looks to small are you saying in length ?? surely the steel didnt just arrive, somebody measured the span and ordered it? your builder? I cannot imagine he took this of the drawing either, either the SE or the Architects.
not sure how far you have advanced but it sounds like you would be able to go backwards and end up with what you find acceptable. Unless that is there is something structurally you are not making us aware of.
Apost of a picture and possibly the SE drawing, calcs, or sketch may be of use.
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