I have just finished patching my tank ,75 gallon with the same holes in it. I went to my local glass shop and had them cut me a piece of glass 10 inches long by 5 inches wide.....now this is what you need to do....make sure your glass piece is the same thickness as your tank, or a little thicker.. The glass on my tank is 1/4 inch thick so thats what i went with...nothing thinner than that !!!!!.. Next you need to scrape any residue from where the holes are ..i used a new razor blade and got up all the old glue/silicone that was on there......next you need to clean off bolth the tank and the patch of any residue and oils.......now this part is very important....you need to buy 100% silicone !!!!!!... And use the clear stuff ... Now lay a nice bead of silicone around bolth holes ,,,then a bead of silicone around the patch...now you lay your patch down over the holes ....what i did next is put a book down over the patch ,then put about 20 pounds of weight on it for 1-2 days... I used a dumbell. ..then take your weight off of it,and also the book...now you take your silicone and lay a bead of it all around the outside of your patch work and let it cure for a few days.....you should have no problems from here on in !!!!...
Good luck, and let me know how it worked out for you....tomorrow i am going to fill my tank, its been a week of curing time for my patch and its ready now.