I agree with the good answer of Dr Berillo. In addition to that I would recommend to use the following monomers in the water phase:

N-isopropyl-acrylamide or N.N-diethyl-acrylamide to use LCST effects. 

A variety of possible issues-

1) Gel is too dilute, slightly lower molecular weight and functionalization than in the paper may mean that instead ofthe weak gel they get you get no gel.  Higher conc may be fine.

2) Oxygen inhibition - degas solution or saturate with nitrogen before irradiating.

3) Glass cover could attenuate the light excessively

4) Your irradiation intensity may not be as strong as the paper.

5) As others note above, you can copolymerize to improve reaction efficiency.  We recently published in Macromolecules on copolymerization of methacrylated GAGs with small levels of PEGDA.

Good luck!

You wanted to prepare crosslinkable gelatin, so why to add low-molecular-weight crosslinker? 1-2% of monomer can gel itself. First, you need to know the real content of methacryloyl units (NMR) in your polymer and real molecular weight (see first comment by prof. Gehrke). Than, we can answer your question... And, of course, this is probably problem of oxygen. How did you remove it? You can also try APS/TEMED (standard) initiation system to compare the initiator efficiency.

Thank you for the suggestions. I am preparing a new sample and will do NMR analysis so it should be easier to figure out what I'm doing wrong.