"How could I mix in native soil without damaging what has already started?"
You really can't do this easily. You risk damaging the fine feeder roots these plants have started to produce. You could add a layer (not too thick) over the top of the existing 'soil' and that will work its way into the underlying Amend soil over time and with watering.

While it may not be an ideal situation, many gardeners grow in straight compost or the equivalent in raised beds without major issues. 'Lasagna gardening' is essentially growing in not fully decomposed sheet composting and seems to be extremely popular and at least moderately successful.

There is enough in the Amend (that name should have been a clue that this was not potting mix!!) to retain sufficient moisture levels and adequate nutrients to keep your plants happy for at least this season. Before you plant next spring, add garden soil (or topsoil or garden planting mix....something with real soil in it) to the raised beds and mix in thoroughly. You may also need to add in more compost as well as organic matter will dissipate over time and need to be replaced. But the mineral content of real soil is important as it will provide a lot of minor elements necessary for strong plant growth that are not available in just compost or a compost-like soil conditioner.