I'm baking a birthday cake for dh - recipe states the mixture is to be divided between 2 tins, but I've only got one tin so have put it all in that. Ho much longer should it take to bake? Has already been in for 10 mins over the 20 mins in original recipe and is still uncooked in middle. PLEASE help me avoid yetanother baking disaster (my baking always seems to end in disaster!!) Thank you!