I find sometimes, if I do something right, to mentally really praise myself and to attempt to dwell on that good aspect as long as possible to remind myself I am not all bad.
Self sabotage is a serious thing, but I find that it just makes things do much worse so a step at trying to stay strong and getting help and avoiding what your self sabotage is can help at least eliminate one of the sources of anxiety.

Otherwise, I am pretty much on the same boat so I am still trying to figure it out myself. As hard as it may be, try to relax and accept that you did your best based on your capabilities and that you will try and work at it for next time. We can be such stiff judges of ourselves, but at least finding something that can relax you can help ease and clear your mind a bit, even if at first the lasting effects can take time.

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