I started leaking about 16 weeks. And like you couldn't resist having a squeeze. I'm now 39wk 1d produce colostrum like a Gernsey cow and have to express about 3 times a day to keep my boobs from feeling like they are going to explode. Have periodically chased my DH around the house squirting him with milk (I have a sick sense of humour and it amuses me that he gets so freaked out about it) and can DEFINITELY say it's not caused me to go into pre-term labour (have been expressing 3 times a day for a couple weeks now at least).

So I wouldn't worry too much about it. If you are squeezing them and you feel a bit of a contraction, then just stop.