There are several halachot which deal with the requirement to cut tzitzit. One is that the strings must be cut from the spool before they are put into the garment (Shul”A, OH, 11:12), another is that after tying they must be cut to 1/3-2/3 (Shul”A OH 11:4, 11:14 – see esp. Rama on 11:14). The Mishna Berura agrees to these cuts but notes that “one should cut with his teeth and not with a knife” (MB 11:61). His language is one of preference not absolute obligation; and surely the final product is not made invalid by the use of a “knife”.

And so, while we use ceramic scissors, I believe that for one who does not have such an option, can use regular scissors, for the d’rabannan requirement of 1/3- 2/3 clearly outweighs the custom of not using a “knife”.

Your tzitzit are 100% kosher.