מדי העבדה means more than is sufficient for the needs of the work.
ויכלא is an expression for withholding.
והמלאכה היתה דים (lit., and the work was their sufficiency — was enough for them — for all the work) — this means the work of contributing was the sufficiency of (was enough for) the workers at the Tabernacle, for all the work connected with the Tabernacle to make it and even to leave some over. • והותר is an infinitive similar to, (Exodus 8:11) “[But when Pharaoh saw that there was respite] he allowed his heart to be hardened (והכבד)”; (2 Kings 3:24) “and they smote (והכות) Moab” (infinitives used in perfect sense).