If you used a sufficient amount of tissue, which would not dissolve upon contact with moisture, and as long as you checked thoroughly and turned your finger while checking, you may consider the hefsek valid. This, of course, is based on your statement that the hefsek came out clean. Please note, however, that this matter is debated among halachic authorities.

As you yourself stated, in the future a hefsek should be done only with a cotton cloth. It is a good idea to get into the habit of carrying a spare packet of bedikah cloths discreetly in your bag so that you always have one available. White cotton underwear or undershirts can be used if you do not have a bedikah cloth. When a bedikah is done with tissue because there is no choice, it is advisable to perform another bedikah with a cloth if there is still time later before shkiah.