お前、心配かけまいと無理してるんじゃないだろうな
From what I can understand from this is probably
"You aren't doing anything unreasonable right?"
How does the 心配 (worry) fit in here ?
I understand that Verb dictionary form + まい = denial/negative
However this is not a dictionary form so how does is work here
「お前{まえ}、心配{しんぱい}かけまいと無理{むり}してるんじゃないだろうな。」
「かけまいと」 means 「かけないように」.
I understand that Verb dictionary form + まい = denial/negative.
Your understanding is only half-correct. The verb form that can precede 「まい」 depends on the type of verb.
Type I: Dictionary form of a 五（四）段 verb & subsidiary verb 「ます」
Type II: Imperfective form of a 上一段・下一段・カ行変格・サ行変格 verb & subsidiary verbs 「れる・られる」 and 「せる・させる」.
「かける」 is a 下一段 verb, so you need to use its imperfective form 「かけ」 to attach 「まい」 to it.
"You're not overstraining yourself, trying not to cause me to worry, are you?"
Other examples:
Type I: あるまい、言うまい、行くまい、話すまい、戻るまい
Type II: させまい、されまい、しまい、もらえまい、くれまい
NOTE: "Type I" and "Type II" are the names I just created for the purpose of answering this question.
