From this manga panel:
I'm having trouble with understanding「ヘマッたことが多すぎて」
I guess this to be "The messed up things (I did) are too many"
I think ヘマ = blunder, and こと = generic "thing", but I don't understand the ッた between them.
It's the past form of a slangy godan verb ヘマる.
e.g. やる → やった Likewise, へまる → へまった