I had a hair cut with scissors and use TOPPIK after FUE transplant. Any suggestions?

The simple answer is YES.  You can use Toppik.  It would not interfere with the surgery.  See the post (LINK below) on Baldingblog about use of Toppik after surgery.

It is safe to get a hair cut 2-3 weeks following the surgery as the grafts are fully embedded. You can use Toppik also provided you do not have any irritation on the scalp. If you do get, then you should wait till all the crust are shed off and then start off with Toppik once again.

Be sure to ask your specific surgeon for his or her recommendations on use of topical keratin agents like TOPPIK as well as hair cuts.In general, any of the nearly 2 dozen hair fibers on the market are fine to use after 2 weeks following a hair transplant. 10 days is likely fine provided a patient has done a very good job with post op care and has kept crusting to a minimum. Provided daily washings continue to be done, use of these fibers even as early as 10 days is usually not a problem.  Irritation is the main issue; infection is very rare but not impossible. As far as hair cuts go, waiting 2 weeks to 3 weeks is usually ideal. Grafts can still be dislodged at the 7 day point. 

usually it is safe to have a hair cut after three weeks. You can start using topic after two weeks when the scans are healed and have fallen off. 

Toppik can be used after the crusts are gone from the recipient area. By16 days, this should be the case. If you use Toppik wile there are still crusts present, the fibers can get under the crust and cause infection or irritation. Crusting either comes off the day of the day or the day after surgery,
or you must wait until they fall off. We always wash the patient's hair the
next day as a service, and after the wash, they have no evidence of any crusts
which they can maintain for the duration of the healing process. If you try to
actively get the crusts off after a week, you can pull out grafts, so once the
crusts become secure, you must wait until they fall off. At about 2 weeks, you
can leave the shampoo on your head for 5 minutes, and then gently, very gently
rub the crusts. The wet crusts will probably fall off over a period of a few
days after you start the process. Pulling off crusts, pulls out grafts.

There are no 100% guarantees, but it is probable if there is no crusting and
you did not pull out the graft (and it shed on its own), a hair with a bulb
after 12 days will leave behind the growth center.