Can I reclass to a 42A if my GT score is not high enough but I have been working for 42A position for almost 6 months?

We are in the process of investigating an AGR who did just what you are suggesting; reclassing to 42A without the requisite GT score. It will not end well for that AGR.

That said, in any state there are more AGR jobs in 92Y than 42A.
But 92Y and 42A typically combine to make up a third of all enlisted AGR jobs in a state. If you are an AGR with two MOSes, those are the two to have.
There is a BSEP course at NG PEC for raising your line scores. AD posts also offer the course if there is one near you, and you can just use self-study to increase your score.

Personnel wishing to reclass into an MOS need to meet the requirements the same as a new Enlistee. Regardless, you need to speak with your Career Counselor about this. Also, there is a course you can take to raise your GT.

The best thing to do is take classes to raise your Asvab scores, without that it would be hard to reclass into a 42A slot. Sorry but from my experience there is no getting around it, I would also check and see what would it take to be awarded the 42A as a SMOS