Yah, I hate to say it, but I think it is unlikely you'll get down to your target gravity with that yeast. Munton's website specifies that their basic yeast (as opposed to their premium gold, or whatever it is called) is not suitable for all-malt fermentation, let alone for relatively high gravity brews such as yours. My first batch was from a Midwest kit, and I did some research when it stalled out around 1.020. For dry yeast, I would recommend Fermentis US-05 for a brew such as yours; just rehydrate with boiled, cooled water and pitch. As long as you let it ferment out completely (i.e. same FG reading after 3 days, and give it a few weeks to get there), you shouldn't have to worry about exploding bottles on account of added yeast. Also, as long as your volumes were about right, you shouldn't have to worry about forgetting to do the OG reading, because with extracts the OG is extremely predictable.