Since ヒヤヒヤする is a verb, that I haven't really been able to find in dictionaries with English meaning. It seems to mean roughly to be nervious/anxious/afraid of something.
But that is kinda messing me up on getting the proper meaning of the following sentence.
Context is that two people have been sparing. And this is what one participant is saying to another.
I think the speaker is saying they were afraid anxious that they might hit the other side too hard.
At least that's how I interpret てちゃうか.
Although it could also be more that she was nervous because she was thinking all the time thinking "Did I hit him "fully" or unfortunately".
As of right now the provisional translation is:
I was afraid, thinking that I could hit you for real.
Which I don't think is exactly right.
So yeah, this is rambly way of asking what would be the proper translating of the above phrase and how てちゃうか and ヒヤヒヤしました work here.