Im trying to get over my obsessions.In Salah sometimes I keep getting thoughts that Im not doing it right.In Sujood the middle part of one finger was not touching he ground & I started getting these thoughts & continued Salah. Then I thought I should have touched the finger to the ground. Is my Salah invalid?

No, as you seem to be an OCD patient.
You have to ignore such thoughts and wiswas.

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