Delta has an anti scald feature. I very delicate little valve that stops water flow unless it has pressure on both sides.

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Are your walls still open? I assume they are as you'd be unlikely to close them up without having had tested your water flow. Here is what I would do.
1.) use the orange plastic C shaped release tool to depress the white plastic ring on the shark bite fitting that you have on the delta side of the Delta-ShowerHead connection.
2.) Carefully and slowly turn water on and see if water is exiting the fixture where you expect it to.

IF yes, water is coming out of the delta fixture then you know the flow problem is somewhere between the delta fixture and your shower head.
IF no, water is not coming out the delta fixture then you need to re-access how you connected the supply lines to the delta fixture.