He was in trouble. Deep trouble. One might even consider it to be serious trouble.
The automatic response to that thought 'no, Sirius trouble', had Peter cringing in an awkward reaction, but it was actually a rather good description of his current situation. Yes, perhaps he had been a coward and a bad friend by betraying James. But really, what choice did he have? He was being threatened by Voldemort himself. Being heroic and chivalrous was all very fine, but it just did not appeal that much once some madman pointed out what fine snake food his your testicles would make, and would he like to prepare them himself? Nagini did prefer her testicles salted and with a dash of oregano. Once the dark lord had mentioned that the frying pan was over there, in the corner, Peter had immediately blurted out 'Potter cottage in Godric Hollow' before he could even think about gathering some courage or doing the chivalrous Gryffindor thing.
So, betraying one of his best friends had seemed a logical choice at the time, but sadly the situation had not improved afterwards.
Of course Peter had tried to hide (he realised he would have to explain quite a bit if something happened to James, Lily and little Harry, and that no matter how events turned out to be it would be much, much better for him if he were somewhere else just being inconspicuous), but apparently the old house of his grandmother was not the best place for that. Once the wards had warned him that someone was approaching Peter had run faster than he had ever run before. While running he just seemed unable to think clearly. His head was a mess of random thoughts circling about, from remembering playing hide and seek as a little child and always being found first to how he was happy that Sirius had never played Quidditch as a seeker because his attention span was just too short (thank Merlin for that). Peter had this vague idea that he was a wizard, not an untalented one even, and still he was utterly unable to think of any spell besides reparo, and well, that was not very useful at the moment. 'A spell' he thought, 'any bloody useful spell will do', but absolutely nothing came to mind.
Peter dashed around corners, hurried past muggles, almost tripped over a stroller, and suddenly he was cornered. Just his luck, running into a dead end street. Peter wheezed and puffed (he normally did not really bother with such tiring things as 'exercise') and he saw an enraged Sirius coming closer and closer. While Sirius started to scream and yell Peter caught his breath and suddenly he had one of the few epiphanies he would ever have. They were the only two people, beside Lord Voldemort and the now very dead Potters to be accurate, who knew who had been the secret keeper of the Potters cottage. So, as long as nobody believed Sirius, or if Sirius was sadly unable to tell his version of the events, Peter was all settled and save.
Mysteriously enough this is where the epiphany apparently ended, because hiding out the rest of ones natural life as a rat is not exactly an ideal situation and can not be recommended in any similar situation. In the years to come Peter would often be angry at himself for being such an impulsive idiot. His wandwork had actually been quite good, confounding the muggles, slicing of his own finger (that really, really, really hurt) and using almost all his magical energy to cast the blasting hex of a lifetime. The following explosion was enormous. Peter turned himself into a rat as fast as he could and then took a second to just enjoy the results of his spell. The whole street had turned into whirlwind of chaos, with people screening and crying, blood and random bits of people lying everywhere and those who had been closest to the strange screaming men in cloaks were lucky if they were alive.
Peter felt strangely calm, as if he was in the eye of the storm. He heard the screaming, crying and the closer coming sirens from the muggle fire pliese arms (as he vaguely remembered them being called) as if they were being blocked out by some pretty decent earplugs, or a mediocre privacy spell, and only later he would remember the awful smell of blood, smoke and sewer and throw up. He sneaked into the nearest open pipe and walked away quietly without looking back even once.